I had a support call yesterday where the computer was highlighting things and deleting them while the user was going back to change things in a document. I was initially suspecting either a faulty shift key or a double-click setting causing things to be highlighted. When I looked at the user's screen I recognized the block cursor and told him to press Insert.

I haven't seen that or heard of it happening for probably 10-odd years now. Didn't realize it still worked in Windows 10!