Just open Dolphin and copy a file by drag'n'drop either over split view from left to right or between two instances.

I always get an immediate crash with the following output in the shell:

kf.kio.workers.file: copy() QUrl("file:///home/user/file1") to QUrl("///home/user/file2") mode= 436
kf.kio.workers.file: copy() QUrl("file:///home/user/file1") to QUrl("///home/user/file2") mode= 436
KCrash: crashing... crashRecursionCounter = 2
KCrash: Application Name = dolphin path = /usr/bin pid = 19964
KCrash: Arguments: /usr/bin/dolphin 
The X11 connection broke (error 1). Did the X11 server die?
KCrash: Attempting to start /usr/lib/x86_64-linux-gnu/libexec/drkonqi


…but X is not dead in my case. Must be something internal. I hope you can reproduce it.