I've been seeing this strange bug in recent versions of Dolphin. Note that it may be difficult to reproduce on demand, and getting this exact effect may take a bit of trial and error. Here is what I noticed so far:

If you select a file or directory, press the delete button, then immediately hit the enter key, Dolphin permanently becomes unresponsive. It does not eat any CPU unless most freezes of this sort, but the window is no longer painted and you must kill the process to shut it down.

This would appear to be caused by the confirmation prompt ("do you really want to delete this item" message) when enter is pressed right before the window pops up. It looks as if the dialog forgets to inform the main window that it has been closed, so the parent process still thinks the confirmation prompt exists and that it's waiting for you to answer it.

To reproduce: Select any item in dolphin, then hit delete quickly followed by enter. Enter must be pressed the instant the confirmation prompt appears, if not a few moments before that. If you keep doing it at various time intervals, you should eventually see Dolphin freezing and no longer responding.