I did some changes in the CSS files of some Blocks. (copied it to application folder first) Testimonial is one of it. Everything is showing up fine. After about a day, the old style is showing up. Clearing Cache is fixing it again for an day. Disabling theme css cache is fixing it completely, but i want to turn this caching on again. Another wired thing is, that i tried to change the CSS files also in the concrete folder (in updates as well) and this blocks are not modified by the theme i use. So there is actually nowhere the "original" css file which is showing up after day with them css cache on.