On Kubuntu 12.04.01 I had my settings to restart previous session on boot. It has now happened a couple of times where the desktop becomes very dysfunctional upon login---the tray was frozen, many programs would not start, etc. I rebooted and the problem was still there, but I noticed that there was a Kate process trying to start on boot, and never showed up on the tray or elsewhere. I found the process by ps, killed it, and then the desktop returned to functioning as normal. This has now happened twice, so is somehow reproducible. However, it might be that I was using Kate under gksudo when the computer previously shut down. I currently changed my settings not to restart the previous session to avoid this bug.
kate version: 4:4.8.5-0ubuntu0.1, according to Muon.
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Ubuntu 12.04 (precise) reached end-of-life on April 28, 2017.
I'm setting the status of this bug to 'Incomplete' as it's not seen any activity for some time. If this is still an issue when using a currently maintained release of Ubuntu then please let us know which one(s) otherwise this bug report can be left to expire in approximately 60 days time.