Welcome to the RStudio Community! We're glad you're here. 
That sounds very frustrating! I had a similar issue in Microsoft Excel a couple years ago, where Alt + Page Down would insert a heart shape in whatever cell I had selected. Very annoying! I hope there's another way around it, but the only thing that fixed it for me was when I upgraded from Windows 7 to Windows 10.
I think it just had something to do with the interaction of my keyboard/computer/OS. Sorry it's not much of a solution, but that's my experience. Hope you find an answer!