I don’t know when I started having this problem, my tiddlers were transparent to start with. But now you can see in the screenshot that there’s another opaque layer beneath the transparent tiddler-frame. You can see the border radius of the transparent layer on top of the square-edged opaque layer.
I thought maybe it was a plug-in I installed, so I disabled them but it didn’t do any good. Does anyone know how to fix this?