bug about gpu consumption

hi, when i open 4 channels in the same screen, i have about 80% of gpu usage.
if i press the - button, the one from the three on the top right (minus, square, x),
i have a reduction of gpu at 60%.
when i have try TvMosaic (other program for see television), i have also a
high percentage of gpu, but when i press the - key for disappear the screen,
the gpu go to 1-2% only.
why progdvb cannot do the same ???