When using a stock install of the latest Kubuntu 15.10, the dialog that pops up (for example, when confirming from the user if they really want to delete a file, or if they really want to apply a setting or discard it), the dialog freezes with no content being displayed inside it (see screenshot for example). It stays like this for a while, about 15-20 seconds, during which it can still be resized and moved (but not closed). After a while the content eventually displays and the dialog behaves normally again. Happens with most applications on a stock install (Dolphin, Kate, Konsole, etc.)

http://imgur.com/oRAbQET

Reproducible: Always

Steps to Reproduce:
1. Open up systemsettings5, with a USB webcam connected to the computer.
2. Change a setting.
3. Navigate away from the tab where the setting was changed WITHOUT applying the change. 

Actual Results:  
An empty dialog pops up (transparent), that populates after a certain amount of time. During this time it can be moved and resized, but not closed.

Expected Results:  
The dialog should be populated right when it pops up.

So I took it upon myself to debug this issue, and opened an application (systemsettings5, in my case) under strace. When I change a system setting and then navigate to a different tab, thereby making the confirmation ("do you want to apply, revert, etc.") dialog appear, I can see that the strace stalls at the call

open("/dev/video0", O_RDWR)

I guessed that this has something to do with the Logitech USB webcam that I have, and so I disconnected it to see if the issue changes, and indeed, it vanished away! All the applications that previously suffered from this work fine now! I do not understand why the entire framework would be required to check for an accessible webcam.