Same here, except I didn't just noticed it.. Its been like that on mine for a while now.. I just thought it was a known issue that clockwork didn't properly wipe dalvik .. Am I wrong or is that still the case?
I just spoke to the developer of the ROM I use and he says it does work. He said it's a bug that just doesn't show you it actually happening but he can confirm that it does work through various tests he's done. That would explain why there's always a hesitation when I hit clear delvik. I guess it's hesitating cuz it's actually wiping it but for some reason it's not showing.