My r9 280 goes back to base clock of 827 almost every time when i alt-tab out of the game. I set the overclock to 1040 with +20% power limit, but it happens with stock 933 boost clock too. Temperatures are in check, latest drivers installed. It happened with older drivers too, on win 7 and win 10 i have the same problem. The only thing that fixes it is restarting the computer.