Howdy Bob,
That should really not be happening. That setting is stored inside of the wp_options table along with most of your settings (the option_name is “tribe_events_calendar_options”). Having done my fair share of upgrades, I have never seen that before. Since only one of the settings is changing and not all of them in that serialized array that narrows it to probably two possibilities:
1) Do you have other admins on your site? Might one of them be changing it?
2) A plugin of your theme is for its own reasons changing this setting upon save. I bet it “reverts” any time you visit the Settings page of Calendar. It could be that one of your plugins has a JS script for instance that is setting some element to month value in the backend. But, in this case it is running on a page it was not intended to.
Either way there is no great way to override that setting other than the settings page. I recently tried for an unrelated script. In the future we would like to add some filters to make it easier to adjust the default view from a functions.php file or your plugin, but for now it’s not really doable.
I hope that info helps!
– Brook
