More OT:
people are saying that in this (https://yadi.sk/d/8cpYUf7bjonE3) version of CM12.1, USSD works. Haven't tested it though.
"I offer you a mod firmware based on the firmware from BuGi (cm12.1). Who does not know - in the firmware are displayed correctly Ussd requests.
What changed...
You know when on KitKat you switch to art libraries and then reboot always takes a while, that I think is what happens by default in 5.0.2 (haven't experienced such a thing on 5.1.1)
Yes, you can but Chinese servers are not always reliable, so the connection might stop and start again, but some bite might be wrong, download managers do help avoid this. And I meant it as a download manager for Android :)
You can't just state an outcome and label it a problem. You should instead explain very carefully what you have done in order to drive your device in such a condition, so that anyone willing can consider helping you indirectly, rather than asking you "oh, what happened". I can think of at least...