I think it has always been like this. Moving bones in setup mode is incrementally applying compensation to the weights. With such extreme movement, the vertices are moved to positions that lose information about the original pose. Then when you move them back, the resulting pose is identical (or not even close). We will still look into what can be done, but I don't have high hopes. I believe Shiu created an issue (but didn't link it here, bad Shiu!).
