Also to add to what others have said, if you file an issue (which I'd encourage) but even if you don't, it's hard to investigate without some steps to replicate.  The issue template has a list of questions to prompt you to think about the information required - but basically, what software (and versions) are you using on your computer?  What NVDA add-ons are you using (and if you restart NVDA with add-ons disabled does it still happen), and if you turn my computer on, and ensure NVDA is running, and I'm using the same add-ons, what specific keys can you press to replicate the issue.  With that information, I (or someone else), can try exactly the same things and see if it happens.  If it does, then I can produce a log and experiment and try to work out what is going on.  If I can't, then what might be unique about your system - and in that case, a log (at debug level) might help us ascertain what is going on and what is different about your system.