Use a restpose Animation (optional and additional)

When you enable “use Bind Pose” then it often also makes sense to apply a reset animation which enforces the Bones to be placed at their exact anticipated restpose locations. However this reset animation must run constantly as a low priority animation (priority 0) to make sure the bones always find their way back to their optimal location after any other animation has terminated.

Avastar is capable to create the Reset Animation and provide a ready made LSL script that you can add directly into your SL Rigged mesh:

Generate the Reset Animation and a Reset LSL script

You will use a restpose Animation when the Bone optimizer could not place the bones correctly. This may happen when you used a custom Shape while creating your edited rig in Avastar. In that case it may be possible that SL places the bones to slightly wrong locations which can be corrected by using the Reset Animation.