Independent backgroundalpha and textshadowalpha, please

Hi!
when I set background="false"
I set textshadowalpha="1" and the shadow text looks good!
but when I set background="true" and backgroundalpha="0.1", even if textshadowalpha is set to 1 the shadow text looks like a 0.1

so it looks like the textshadowalpha it taking the background alpha value when the background is enabled.

Is this a bug or a feature?

Thanks!