I have been using the WP Maintenance plugin for some time now. I will be relaunching my site in early June, so I need to have this plugin activated a bit longer.
Recently I installed the BackWPup plugin, and every time a backup is made, BackWPup disables WP Maintenance. I have to switch it back on every time a backup has been made (usually at 3 or 4 o'clock in the morning), so the site is online for a couple of hours before I get back to my computer.
Eventually, I am going to switch WP Maintenance off, so in theory this issue does not need to be addressed (at least not as far as I am concerned). Maybe other users will find it useful if the bug would be resolved. However, I still wanted to bring this to your attention. I've already informed the owner of WP Maintenance about this bug.