In core.php I find the following
Using release 1.1.1 (and confirmed with 1.0.1) I followed the above directive.# To make Mantis 'offline' simply create a file called
# 'mantis_offline.php' in the mantis root directory.
# Users are redirected to that file if it exists.
# If you have to test Mantis while it's offline, add the
# parameter 'mbadmin=1' to the URL.
Page 'mantis_offline.php' is properly displayed as expected. If I add ?mbadmin=1 to the login.php url, I do see the login page, however, I cannot login to my bugtracker. I get bounced back to the offline.php page.
Is it just me, or do others see this. I could not easily find an issue in the bugtracker about this problem.