I have the same problems as rest of you, and i found out what cause phone to turn itself off and block. SD memory card.
Dunno if its specific sd card brand that cause problem or is slot for memory card itself.
I think my zte racer II have kingstone 2GB sd, if some1 can confirm what brand is your card, is it all the same or mobile sellers put sd from their own stock.
Ill try to replace my current sd card with some other brand and see if it fix this sd card issue.
Ill report here for updates.
PS. If your phone block itself again, try not to remove baterry, remove only SD card and try to power up to confirm you have that specific problem.