Problem description: 

Steps to reproduce:

[1] Copy the German LibreOffice Download page (http://de.libreoffice.org/download/) to your PC. I did this with Firefox: "Save as .." function. A file with the name "Download » LibreOffice.htm" and a directory with the name "Download » LibreOffice-Dateien" are created. The directory contents 7 files.
[2] Start LibreOffice.
[3] Open new text document.
[4] Insert some words.
[5] Save document. I named it "testfile.odt".
[6] Add some more words, but don't save the document.
[7] Open the copied HTML file ("Download » LibreOffice.htm") in LibreOffice. Wait. Message: "Due to an unexpected error, ...  The following files will be recovered: testfile.odt". (By the way: Sometimes there is a nice visual effect if you move this message window with the mouse.)
[8] Click OK. Message for a very short period of time: "documents are being saved" or similar. Then LibreOffice is closed.
[9] Start LibreOffice again. Message: "Press 'Start Recovery' to ...", two documents are listed: "testfile.odt" and "Download » LibreOffice.htm".
[10] Click "Start Recovery >". Recovering process starts. Both files are marked as recovered. Message: "Recovery of your documents was finished".

From now on I observed different behaviours with variations:

[11a] Wait. The message changes to "Recovery of your documents was finished. Click 'Finish' to see your documents." Wait. A new message window is opened: "Due to an unexpected error ...  The following files will be recovered: "testfile.odt" and "Download » LibreOffice.htm". Sometimes this message is already displayed if you wait and don't click 'Finish'.
[12a] Click OK. An unfinished box is displayed (not always). The Windows sandglass appears if you move the mouse over this message box. Another "OK" click does not have an affect. 
[13a] Close the message box: click red cross. A Windows message appears, that the programm does not react. Now the only way to go on: Close LibreOffice at once. Wait. Then you are asked to send a problem report to Microsoft.

or other possible behaviour

[11b] Wait. The message box closes. LibreOffice is no longer active.

You can start LibreOffice again and again beginning with step [9], the behaviour is either equal or similar as described. The only way to exit this loop is to cancel the recovery after step [9]. 

Then LibreOffice behaves as follows:
[C1] Cancel recovery. Message: "The automatic recovery process was interrupted..." is displayed. You are offered to save the document "testfile.odt".
[C2] Click save. Wait. LibreOffice starts with an empty text document. Sometimes the document "testfile.odt" is saved as "testfile.odt_X.odt" (X: Number), (It is not saved as testfile.odt as expected.), sometimes it is saved not at all.

Comments: 
[1] With Version 3.4.5, the described behaviour does not occur. But I did only a short check.
[2] The recovery process does not recover changed files, but you have to cancel the recovery in order to get a chance to recover your changes.
[3] If the document is not saved in step [C2] the changes of step [6] are lost.
[4] You have to know that the recovered file is renamed. I did not. Only because I dealt with this bug, I found my lost document.

Platform (if different from the browser): 
              
Browser: Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.9.2.27) Gecko/20120216 Firefox/3.6.27