Hi utu
Sorry, I don't know if I can help much, though my problem sounds very similar to the one you reported.

What would happen is that often when i had several [3 or 4] .odt documents open at once - in separate windows that is - and I would be cutting and pasting blocks of text and maybe diagrams as well across into these .odt documents from [mostly] iceweasel but sometimes from icedove.

Then the whole screen would freeze up and often even Ctrl-Alt-backspace would not get me out of it and i would have to power-off with the switch to turn the machine off and then restart it. Often Libre Office was unable to recover the documents when i next fired it up so the work was lost altogether.

I think if I remembered to keep only one .odt document open at a time then the freezes happened less often and I don't remember it ever happening when i was only entering text directly from the keyboard -as opposed to interacting whith other programmes via the clipboard.

Even if the whole system didn't freeze, what would often happen is that when i closed each LibreOffice window then its tab would remain in the window-list part of the LXpanel and I would have to reboot to clear them from the panel. But at least on those occasions it seemed that I was able to save and close the files properly and so I didn't lose data - it was only the tabs from each window left behind in the no longer functioning panel that were the problem.

Sorry I don't know enough to start looking for the real cause - like whether they are basically a malfunction of LXpanel or of LibreOffice. I haven't [so far] had any similar problems with Open Office 3.3.0 running with the exact same LXDE set-up. Just to remind you - I am using a hard drive install of Knoppix v 6.7.0 DVD.

I hope one day [soon] someone will find the answer.

Best wishes, John