Problems with "Internal page cache" module. It still caches the block even if caching is disabled for that particular block!

I place a form in a block and i'm using image capcha in the form.

So i disabled caching (via UI) for that particular block to make sure captcha image is re-generated . The problem is that for anonymous users image generated is always the same, it means it takes it from cache. If i disable "Internal page cache" module everything works perfectly, also the problem appeared in beta10 since "Internal page cache" module was introduced. Please help!