I upgraded last week to 3.5 and have begun to notice some odd behavior.
When typing in "Head HTML" at times the text jumps down a line (taking out the line number) and then I can't delete the extra spaces. When I try, the cursor remains on the lower line, but begins taking out chars in the line above and pulling earlier characters down into the lower line. Quitting Hype and reopening it did not change the behavior. Other text programs on my system are behaving normally.
For now, resorting to using Sublime and then pasting over the existing text in Hype as the more I try to do within Hype, the less usable the code I had in there becomes.
It starts writing vertically down the side of the window, also. This from within a comment block.