Being unable to play video while charging, strange

I thought I’d prepare myself with the tablet for holiday season and started to convert avi’s to .ogg with VLC or h.264 with Handbrake or DivX converter. It is a bit of a hassle, but I guess I will find the best suitable videoformat for it.
After testing several videoformats I noticed the battery is getting empty pretty fast (which I can imagine since the screen is the most energy costing part). So I hooked up the charger, but while charging it is not able to play video’s or music. Why is that?
I hope manufacturers will work around this issue, although I know this seems to be by design, since it is in the l10-files.

Also reported at: https://discourse.mozilla-community.org/t/bug-no-sound-when-tablet-is-charging/515