[heresy]

Yep. Without thinking, I used code for an open source library I had written in my spare time in our proprietary software, and it came up during a due diligence check for acquisition.

Wasn't a big deal in the end, I just made sure it was using a commercial friendly license, but you do have to take care.

If it was a US employer they may have sued me if they didn't think that the OSS code came before the inclusion in the product (which it did).