Bailing out the bathtub

I wrote the previous entry for today earlier. Tonight, C was taking a bath and the drain malfunctioned. The plumber mentioned that this type of drain was particularly touchy and didn't work well. I asked him if he meant the brand (Kohler) or the type of drain (it has a spring). He was not specific in his answer, so I still don't know. The drain worked right for 1 bath, and then it stayed up (open) but could be pushed down (closed) to take a bath. The problem was we couldn't open it up after C's bath. We ended up bailing all the water out to remove the pressure on the drain and then we were able to open it. It was definitely not fun tackling this late on a Sunday night. We are also not sure what to do - this is the drain that is made to go with our bathtub, so we really want it to work. We are hoping the plumber will fix it without charging us. I think that will be a another fight! We are also hoping that this drain can actually work correctly.