Please report these problems including, as Toxaris said, full system details. The developers/maintainers work very hard to get out bugs, but they need to know all the details including every step you take and every other program running on your system.
This can often best be done at:
http://code.google.com/p/sigil/issues/list
rather than clogging up the forums with all the details of your system, once you are sure it is not just a simple fix.