The problem does not exist on all computers.
I have beta2,ext4 running on a P2-350 and it has no problems at all, whereas the 3 core AMD has twice now locked up with no-responsive icons when installed with ext4, but not with ext3.
The other 2 Intel Machines I have, on one I cannot install beta 1,2 on the other beta 1 will install but not beta 2
There is no common denominator to say why.
Thus the question about ext4! This problem does seem to machine related, as I install beta 2,ext4 on 2 different drives and they both locked up, but installing ext3 the system is fine,but I cannot see what relates to what.