The behavior is a bit hard to describe, but its roughly as follows:
When starting to scroll a document in QtCreator using my mouse wheel the document position will jump after scrolling in another application first.

Steps to recreate:

• Open up a document in Creator you can scroll.
• Open up another application where you can scroll through some content (like a web browser or something)
• Click on the other application so that its active/focused and scroll up or down
• Click on QtCreator so that its in focus and try scrolling the document.

It's almost as if what you scrolled through in the other application gets reapplied when you begin a scrolling action in the QtCreator editor. If you scroll down for a bit in the secondary application, then click on the QtCreator window and try scrolling up, it'll jump down before it starts scrolling up again (at least thats what I think is happening).

I haven't observed the behavior in other applications on my system (I checked Clementine, a music player based on Qt4 but I don't have any Qt5 programs to check against.)