Hello,
I was testing it in the version 5.5.4083 of Kentico
CMS and was able to reproduce that kind of incorrect behavior - when I pick a document node to drag it, it jumps above for some reason (it doesn't stay on the mouse pointer). However, the functionality of moving, copying and ordering works just fine. Anyway, I'll pass it to our developers as a bug.
I'm sorry for inconvenience.
Best regards
Ondrej Vasil