I've seen this before. In my case it was just some simple error such as mixing up bean names. I did this once, trying to access a bean from an iterate tag, but there were actually two beans with the same name in the session and it was using the wrong one. It took me ages to realize. I think to find the error you must rebuild your page tag for tag, retesting it at each point.
I have seen things you people would not believe, attack ships on fire off the shoulder of Orion, c-beams sparkling in the dark near the Tennhauser Gate. All these moments will be lost in time, like tears in the rain.