If I scroll down on a file (fore example some lines or pages) with mouse wheel an try to scroll up (back) the it jumps ~50 lines down. I use a logitech mouse and with each step scroll down it scrolls 3 lines down. Witch each step up, it scrolls 49 lines down.
One test is:
– new file
– write 10 lines (or press 10 times return, so 10 empty lines there)
– scroll with mouse wheel up
-> the view of document jump to the end of file, the document show now only the last line.