I've been having this issue for almost 2 years now i think. It used to work normally, then one driver used to broke it and i've been waiting for a fix for a while but nothing happened so far and i'm asking here in case im the one doing something wrong.
I have vtx3d r9 280 x-edition (will list other specs bellow). which is a normal 280, with a stock overclock to 960/1250. The issue is whenever i open anything with enabled hardware acceleration my graphic card locks down to 280 stock values of 855/1250 and 501/1250 on 0% load. When i finally find and disable the hardware acceleration programs/options it goes back to normal behaviour going up to 960/1250 on high load down to 300/150 on minimum to zero load. i usually run the card overclocked on radeon overclock on 1100/1440 for global overdrive and that doesnt affect hardware acceleration. it just locks down the bad boy back to 855. I also tried using other overclocking softwares like msi afterburner and easytune6 but nothing survives the graphic acceleration lock. I do experience artifacting if i am overclocked and hardware acceleration limits to 855, but no artifacts if i stay at default 960. which also means i cannot use any windows 10 store apps because all of em default hardware acceleration with no options to turn off, im limited to non-video wallpapers in wallpapers engine even with hardware acceleration off etc. all in all its very limiting and i would like to see this issue resolved. as i stated at the begining i did not have this issue from the begining, it started becoming an issue with a driver one or two years ago.
i'm running radeon 18.2.2 drivers installed clean with DDU in safe mode which i always do with new drivers. Radeon software properly shows Core clock at 960MHZ as well.
Windows 10 pro 64bit, build 16299
gigabyte 990FXA-UD3 rev 3.0 (maybe its 4.0 if its important i can check the box)
amd fx 8350 processor (never tried or atempted overclocking it because its running without issues so far)
8gb 1866mhz ddr3 ram
2x 1080p monitors
i have latest BIOS version and all other drivers should be up to date.