Bug#858620: okular freezes regularly the whole desktop for 10 seconds or so. Happens quite often.

[Miguel Hermanns]

I have some further information that may (or not) help. If during the
freezing I try to change programs, of course nothing happens. However, when
the desktop gets responsive again, the mouse icon changes and wants to
paste a text document to the next program I click. If it is a text editor
(Kile) or a browser (iceweasel), then indeed a text file is pasted or
opened with extension .desktop.