The taglib is called Wall.
When I say browser, in this case I'm talking about mobile phone browsers. Mobile phones tend to have different browsers, but the taglib wall should handle this.
I've found that in this case wall actually does something I didn't know about. I tried calling confirmSP.jsp from a standard browser that I can check the source code with, and wall is populating the form action.
So I now think that this problem is to do with the wall taglib not dealing correctly with the mobile phone browser type.
Initially when I said at the start of this
thread that the code had action="", this was incorrect as I didn't realise the wall taglib was changing it. Or possibly it was correct and because wall was failing the action was being left empty...
Thank you for the help Vishal and Rosco. I think I need to start looking at whats going wrong with the wall taglib as the error is more likely to lie there.