I have the same issue.
I thought upgrading would have a fix for it. I tried to upgrade to 1.5.3, it went bad and had to restore the site back to 1.5.2
Idea #2 I thought maybe they got all that fixed in 1.5.3.1, it went even worse. Still picking up the pieces from that bad idea.
Idea #3. Do a fresh install of 1.5.3.1 and just copy over the database. My whole site didn't crash so that was a plus. However, it copies the issue to the new install and you still cannot go back to a single store mode and have it work like before.
Hope somebody figures this out soon