Did a foreign languages study affect your fluency in your native tongue?

[Voytek]

I wonder, if you noticed any changes in your native tongue fluency caused by a foreign language study. Sometimes, I have got a feeling that it affects it negatively and I encounter minor problems with my fluency. How abou you?

[moo]

I don't think learning a foreign language has a negative effect on my English , actually the opposite ; it gives me a better understanding of English grammar but one thing I do think can have a negative effect is spending too much time with non natives like marrying a non native and speaking with them in your native tongue constantly, i think that can have an effect on one's native language. I don't mean to offend it's just what i found from dating non native speakers and spending a lot of time with them but everyone is different so i'm not saying this applies to everyone

[Voytek]

I don't think learning a foreign language has a negative effect on my English , actually the opposite ; it gives me a better understanding of English grammar but one thing I do think can have a negative effect is spending too much time with non natives like marrying a non native and speaking with them in your native tongue constantly, i think that can have an effect on one's native language. I don't mean to offend it's just what i found from dating non native speakers and spending a lot of time with them but everyone is different so i'm not saying this applies to everyone

Same here when I spend too much time with Poles who don`t speak Polish grammatically. And it`s very rare to find Poles whose the Polish grammar proficieny is almost perfect.

That`s why I study rather by reading books than speaking with naives who speaks my TL. Reading books in Polish helps me massively to improve my mother tongue skills and I applied this to a foreign language study and it works great.

[James29]

My English spelling is now worse after studying Spanish, but generally I think studying Spanish has made my English better.

[Ezy Ryder]

I constantly find myself at a loss for words (like "arbitrary", "participle", "protagonist", "to humour (transitive usage)", "ink-brush" or "fallacy") and sentence structures (like "in the first place"). Occasionally I'll also try using a saying, just to find out it's difficult to make it work in Polish (like "languages cannot be taught, they can only be learnt").
I can also notice some effects on my accent. Namely:
-Dropping unstressed vowels (I'll sometimes catch myself pronouncing /ˈjɛd̪ɛn̪/ as /ˈjɛ.dn̩/, or /ˈnad̪al/ as /ˈna.dl̩/ (possibly velarised?).
-Realising some stops as unreleased, for example pronouncing /ˈkɛt͡ʂap/ as /ˈkɛt͡ʃap̚/.

Same here when I spend too much time with Poles who don`t speak Polish grammatically. And it`s very rare to find Poles whose the Polish grammar proficieny is almost perfect.

Why so prescriptive?

PS Is it just me, or is the forum having some problems rendering IPA? Especially the primary stress marks look like they're above the following sound, rather than before it...

EDIT: Added some more examples.

[Voytek]

My English spelling is now worse after studying Spanish, but generally I think studying Spanish has made my English better.

My studying of Spanish improved my knowledge of the English grammar because there are many gramatical similarities between the languages and I found a Spanish grammar book more transparent than an English one (the Murphy`s book). It helps me especialy with understanding the idea of articles which don`t exist in Polish. Thank you, Spanish!

[Voytek]

"languages cannot be taught, they can only be learnt"

Here you are, mate:
Nie można zostać nauczonym języka obcego (a singular form), a tylko można się go nauczyć.

[verdastelo]

I'm not as fluent a speaker as I would have been had I not ignored Punjabi when I was learning English. My accent has worsened. But my vocabulary has increased. I can read literary essays and opinion pieces that most natives struggle with.

Details
I learned Punjabi, Hindi, and English simultaneously. They are part of the curriculum in pre-nursery (3- or 4-year-olds). But Punjabi being my first language, I learned to read in it rather quickly. Then the funny things began to happen:

1. I considered reading in Hindi when my parents and other people convinced me Punjabi was the language of the idiots. I started reading in Hindi and loved it; tried with all my might to erase all traces of Punjabi from my being.
2. Then I encountered English and realised it is even richer than Hindi! So , armed with a 1989 edition of Oxford English Dictionary, I worked again to erase all traces of Punjabi and Hindi from my mind by consciously avoiding any contact with those languages. That continued for so many years that today a lot of the time locals mistake me for a foreigner of Indian-descent. My pronunciation is that bad now.
3. Esperanto made me aware that it was wrong to ignore Punjabi and Hindi.
4. Learning Russian has taught me English isn't the only language capable of bearing the weight of philosophy, science, and culture. So I'm reading in Punjabi again and it's helping me in the vocabulary department.

[aokoye]

Same here when I spend too much time with Poles who don`t speak Polish grammatically. And it`s very rare to find Poles whose the Polish grammar proficieny is almost perfect.

It's hard to find anyone whose grammar in any language is "almost perfect". People don't speak or write as prescriptively as they might think they do (which isn't a problem in my eyes).

[aokoye]

The only time my native language (English) suffers is when I'm spending a lot of time (weeks or months) not speaking it or not speaking it as often as I would in the US (or England or...). My accent also changes pretty drastically.