I suspect this bug will just sit here since everything currently just works (TM) but we really should remove the MobileFrontend user module.
Previously this was setup as scripts in common.js were not compatible with the mobile skin and when we enabled the user module originally there were various bug reports due to breakage.
I think it is our duty to force users to think about the scripts they put in their user common.js and make them more future proof.
The question is do we accept the trade-off of temporary inconvenience and do so, or do we make more efforts to prevent scripts from breaking in the first case (e.g. wrap in try/catch blocks)