When generating a checksum for a large file on an external hard drive that can take a significant amount of time, the thread is not exited when the properties dialog is closed. This leads to Dolphin not exiting when its window is closed. To reproduce: 1.) Copy a large file onto a USB stick 2.) Right click -> properties -> Checksum -> Click "MD5" or any other checksum 3.) now close the dialog whilst it's still "calculating" 4.) close dolphin Notice how Dolphin keeps running and consuming CPU and prevents unmounting the USB stick. It's using QtConcurrent::run which doesn't support cancelling, so this probably needs to be rewritten to using QThread (or a KJob?)
There's an another pathological case for this when you accidentally try to checksum a character device (/dev/zero and friends). Unlike the first repro in this case Dolphin will never finish, crunching 100% CPU in the background until you manually kill the process.