Gimp animation player is also a filter??

[Tas_mania]

My first post here. 

I use the Gimp animation player quite a bit to test animations. I've noticed two things recently.

 The animation player ignores dim backgrounds on transparent (alpha) layers.
This looks like a 'foreground extract' filter that appears to be coded-in. It could work as a stand alone filter.

 Also there is an icon in the top menu that says 'detach the animation from the dialogue window'.
I'm not sure what this actually does. Any ideas?