Ok - so I'm the new guy here. Literally. However, I saw this thread and I was having similar problems. I found that I was tying my foam too loose causing my beetles to float "bottoms up". Try tying a little tighter or adding a few more wraps of thread to the body.
I've also experimented with running a length of lead wire along the shank. Seems to work ok, sometimes, maybe.
Just my .02 cents.