I needed to modify block.tpl.php so I could install and use the block_class module. I copied block.tpl.php from modules/system/ and pasted it into mobile. I edited block.tpl.php to match what was required by block_class. I cleared all caches. There was no effect. I pasted the same file back to modules/system/ and the block_class code worked fine.

Any idea why I cannot get my template override file to work?