Although no solution for Karel:
Same problem here, although I'm 99% sure that it is due to running different versions of software on the clock (v355) and on the ESP (v352).
I reflashed the clock in order to get rid of the decimal point and took the most up-to-date software version from bitbucket. (there is no way to download older FW, isn't it?)
So far, I haven't looked into getting the ESP flashed, mainly because I don't have a programmer for it. It'd be most likely possible to flash it using an Arduino?! I guess I should google a bit for it.....