My TV is Samsung, and I have CEC (Anynet) enabled. Before chromecast update I was able to pause/unpause video using TV's remote control, but after update it works only once or doesn't work at all for youtube. If I stop casting, then start again, I maybe lucky to catch one reaction to pause/unpause, then it doesn't reacting anymore.
I tried factory resetting Chromecast, but it didn't help.
Also, as far as I understand, the fw ver. 1.56.291998 is a beta fw, but honestly, I don't remember subscribing for beta program.