Thanks for your help!

Concerning RemoveDuplicates:

Ah, foreach making a copy was new to me, that would be the problem (the Header actually had a reference)!
I will try with a regular loop or non-const iterators…
I thought using threads for the latter be a bit overkill aswell, but would there be a way to use threads for the whole thing? I mean the qSort is O(n*logn), and the "setting 0" is O(n), I don't know how fast removeAll is, but it probably isn't to bad.
Still I need to do it quite heavily and really had positive experience with QtConcurrency in other List-Operations


About the second application:

Do you think thats the proper way to do it? Calling contains() so oft seems expensive to me…