On Windows 7 32-bit, and LO 4.3.0.4 and 4.3.1.2 (using JDBC connector):

1.  Open Base.
2.  Edit form in significant way.
3.  Close LO Base.  More reliably triggers bug if you do not save in advance, let dialogs pop up asking about save.

UNEXPECTED RESULT:  Base hangs, visible in window but does not close (especially if you waited for dialog boxes to ask about save).  Alternatively, if you press the save button in advance of closing Base, the window may disappear but following processes remain running in background and block reopening of all LibreOffice documents: soffice.bin *32, soffice.exe *32, sbase.exe *32.

I began experiencing this problem after applying August 2014 Microsoft patches.  It might have been a latent problem not noticed earlier, or it might have been new with the then-Fresh LO 4.3.0.4.  Did not notice with LO Still 4.2...  This does not happen every time, but it does happen very frequently after editing database forms and queries.

FIRST WORKAROUND:  Kill process soffice.bin *32.  All other processes will terminate, have *not* experienced data loss (save is successful).

SECOND (possible) WORKAROUND:  Save Base document manually, press "close" instead of "exit", in LO main workspace (which pops up next) ask to open LO Writer, exit LO from Writer menu.  This sequence, calling Writer before trying to exit LO, appears to result in normal close.

Filing bug report because another user reported problem finding workaround in LO Ask forum.

http://ask.libreoffice.org/en/question/39496/how-do-i-solve-a-problem-with-base-saving-forms-and-then-not-exiting/

Normal user might have trouble identifying workaround, without workaround blocks normal use of Base for design.  Not sure if this is a problem on all Windows 7 systems, hunch that it is related to more universal problems with some Microsoft August 2014 patches, but not sure.