Unless you have phenomenal recovery abilities, I would say it is bad.It also depends on what your goals are in regards to the lifting and the boxing.If boxing is a priority, I would certainly box first while you are fresh, then do a quick session in the weight room.
I would also throw out there that it depends on your lifting routine and your boxing routine. I know that if I throw on my heavy bag after lifting, it's not bad and in fact can feel pretty good to keep the blood flowing.
