Avond Gijs;
Not sure what's happening really. Could you test some things for me?
1. what happens if you don't inline, does the string get added to the autoptimized CSS-file in that case (guess it does)
2. could you try excluding each of your original CSS-files from optimization, trying to identify the culprit?
We'll see what that teaches us ...
Groetjes uit Lokeren,
frank