Hope this is filed correctly ...
KDE's file open dialogue scrolls horizontally - to me, that has always be a major annoyance. Especially now, as more vertical selection elements are placed in Plasma 5 (e.g. activities switcher), it would be wonderful to have vertical scrolling - at least as an option. Bbut why not make it the default, so much nicer to navigate with a mouse - and just the right thing to do (TM) ;)
With that flaw (it is to me), I never understood how KDEians dismissed other file open dialogues.

Reproducible: Always

Steps to Reproduce:
1. Try to open a file further down the alphabet from a directory that holds more than a few entries
2.
3.
Actual Results:  
You have to scroll horizontally

Expected Results:  
You should have to scroll vertically - at least as an option, but IMO better make it default ;)