Firstly, the SB client does not support being disconnected in that it won't download a bunch of tests and crunch away. The server needs to know you are still out there. It will reissue your work as early as 5 days after not hearing from you. There are other reasons too I'm sure. Read the thread about what is wanted in the new client for more info.
Secondly, SB uses your computer in some fairly uncommon ways. If you are crashing, you may have marginally bad memory.
Thirdly, the blocks done counter resets after stopping and restarting the client. It does not query the server. That being said, the 'blocks' are lost anyway, because blocks per se don't really exhist. They are just a way to divide up the real work (the full test) so that slow machines report work down before the 5 day timeout. The test isn't done and the results aren't useful until the full test is complete.
You do however still get credit for 'blocks' - click your user name in the client to see your stats.