Just updated some modules on a site with better messages enabled and had a bunch of update.php errors. This caused better message to display the popup and "overflow" the screen. I could not see all the messages and could not "reach" the OK button to clear them.
Of course, I have now added update* to the excluded pages... but valuable error information was lost since watchdog does not really capture all the info.
I would suggest a test to see if the system is in maintenance mode before using the popup method.
Maybe a quick alternative would be to have the default settings be to exclude all admin and update pages. E.g. show on every page except:
admin
admin/*
update*
I know I end up doing this for all my admins because they complain about closing the message box when doing admin functions. (But love it for end users).
Fixed
1.0
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Issue #1154416 by UsingSession: Sensible defaults for url exceptions
Added for review about the page update.php (or MAINTENANCE_MODE)
Automatically closed - issue fixed for 2 weeks with no activity.