I deactivated all the modules, and then I activated one by one until I found the module witch made the problems (for me was a clone of xcgallery), for you, it can be other module.
Thrue. If you use XOOPS 2.0.16 you don't need this hack. But after I updated from XOOPS 2.0.13.2 to 2.0.16 I had to modify my old theme to display all the blocks.