Windows "typing" text from clipboard on its own

I'm having a very strange problem that's difficult to describe, especially since it happened while I was caught up in routine. While I was filling out an online form suddenly it felt like windows had a life of its own and it started typing something I've just had in my clipboard into one of the textboxes and hit enter. The weird thing was that it actually typed it out instead of pasting it all at once. I'm not even sure how that's possible and where to even begin looking for a solution so I wanted to make a thread here in hopes someone has encountered this strange issue before. In fact I had i

Question by Vyralator on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.