Hi there Blackcockoo,
You can just copy-paste the text from the file, rather than using the direct file upload. Also you may want to have a look at the thread over here: Mouse jumping/centering FIX.
It doesn’t exactly match the problem as described by Pharah in the original post, but it’s a pretty solid list for any kind of mouse issues, in addition to the links that were posted earlier in this thread already.