Rotobrush reveals transparent area that it shouldn't

1. Use a garbage matte (mask) to eliminate everything in the shot but your actor
2. Apply a keying effect to remove the solid-colored background (green screen)
3. If the actor's feet don't move or don't move very much, just animate another mask around the actor's feet to remove the remaining background
4. If the actor's feet move a lot, then duplicate the layer, draw a mask around the feet, leaving enough room for the feet to move, then Pre-compose the layer moving all attributes to the new composition
5. Open the pre-composed duplicate layer in the Layer Panel (easiest to do if you are in the paint workflow and have rotobrush selected), then eRotobrush just the feet
6. When rotobrush is complete and frozen, use the Rotobrushed layer as a track matte for the keyed copy of the footage, pre-compose both layers, and proceed with the composite.

No rendering is required, only using rotobrush or masking by hand on the part of the frame that can't be removed by keying, and a lot of time is saved. I almost never rotobrush footage that does not have a garbage mask or manual rotoscoping applied. I also color-correct footage and pre-composed it before using Rotobrush to improve edge contrast. 

I also almost never key footage that does not have at least one garbage matte. There is no reason to fiddle with parts of the image that you don't have to, and a mask is the easiest way to do that.

Hope this helps. 

Transparency in computer graphics always means that there still is the RGB info, whether that's the origional data or a generic black fill. Alpha channels/ transparency are merely a means of telling programs that interpret that info to not display or process pixels or gradually blend them with the surroundings. so far that's perfectly normal. If you don't want your cloth, insert a colored solid behind your keyed work, but soemthing will always be there and, to get to the second point, Rotobrush will always make it visible again because it completely replaces transparency, not adds to it. As far as AE goes, everything is normal. In order to combine your data you therefore have to work with duplicate layers, pre,compositions, track mattes and/ or effects liek Channel Combiner to merge that info. In your case of course you would also simply use holdout mattes, i.e. an inner/ outer mask in Keylight to eradicate everything outside the screen that doesn't even need to be removed. so in essence you have several workflow issues here. To recap in short:

• Don't bother with keying if you want to use RB.
• If you key, use a mask and reference it in keylight to eradicate the furniture.
• Combine the result of both operations with mattes, pre-composing and effects.

Mylenium