Come on over and check out Talista's thread she has an excellent dialog going on just this very topic.
It seems that THIS anger/resentment/wanting to be a WA ourselves is just another stage in the process. We spend time (of whatever amount) working so hard to get our WAS to come home and give our M/R the 'old school try'...and then when they do...and our energy is no longer fully focused on getting them to "CHOOSE US"....slowly after the novelty of thier return wears off...all the other NORMAL emotions we have come to the surface.
Anger/resentment etc is a powerful replacement for the previous fear of the unknown.
Once they're 'back' the rose colored glasses come off and WE begin to see the flaws that we convienently forgot existed in them when we were scratching and clawing our way back into their hearts.
They come home with any number of reservations in their mind. They resent feeling guilty about what they've done. They fear never being forgiven, they fear "THE PAYBACK" that might await THEM from us...They fear their own inability to make the R work again, they resent the fact that they will have to face the hideous consequences of their dispicable and childish choices...they can barely look at themselves and they can barely stand to have us looking at them.
It's hard on them too. We are the mirror of the greatest human failings of their life...and now, they have to figure out how to live with themselves and live with us too.
They act standoffish as a defense mechanism for thier guilt. They don't want to appear grateful for the second chance, lest we throw it in thier face eventually. They made the decisions they made because they couldn't face us and tell us what they needed BEFORE they made the choice to fail...so it's foolish for us to think that now after all the collateral damage they've caused that they can rally enough empathy for us when the vast majority of their energy is still focused on themselves.