This is essentially this huge bug in WebKit. I’d call it a bug anyway. You can apply the “thinned out” text look by applying a benign 3D transform to the area with text. That way it won’t jump to that thinned out look on hover. But that’s kind of a crappy fix. Usually you just have to decide what is worse, the thinned out look all the time, or the jump.
Cannot reproduce the problem but what you describe sounds familiar. What andy_unleash wrote should fix the problem, but from what I learnt “backface-visibility: hidden” can have some nasty side effects – at least that is what I remember when I gave it a try.
What I ended up using to fix text-rendering glitches while css transforms/transitions are running is: