I am building out my site, and am noticing that as I build, the CMS is breaking on me. How odd.

I have a section that is three levels deep, and after every refresh, if I try and load the second level, I get an "error loading subtree", which doesn't go away until I refresh again. It seems to only happen if the trees are open when I do a refresh. I did a search, and found some people are encountering this, but no solutions.

Also, if I do a ?flush=1 on the admin area, all the tab graphics disappear, and are just plain text. It often takes 2 or 3 refreshes to get these back.

The weirdest part, to me, is that I can tell when I am going to have a problem, because the "Allow Drag and Drop Reordering" field in the CMS breaks, so it becomes 2 lines (see the attached screenshot). To me this is odd, and it's just the current site I am building that's doing this, and no sites I've done with SilverStripe before.

Anyone have any ideas why this might be, or how I can fix/prevent it?

My server's memory limit is 64MB, which should be enough, according to the system requirements page.