As Phil said, to ensure that the validation errors in other tabs won't appear, it is necessary to restrict the refreshed area and the executed/validated area (which would normally specify with an execId property on the submit event). The tab areas were attempting to restrict the events on buttons within that area so that just that tab is executed, but it wasn't working.
The problems with ExtLib controls using execId was reported in SPR#PHAN8P3LU2 (it effects many controls, including the Mobile Page, and Dojo Tab Panel controls.)
With the fix for SPR#PHAN8P3LU2 in place, then I can create and save content in a 2nd tab even when the 1st tab has missing required fields. For events on controls within the 2nd tab, only the contents of that tab are partial updated and executed.
That fix should be available in the next OpenNTF release.
[That fix will not work for the Refresh Page button though, because that button attempts to refresh the entire page, including all of the tabs, so it will validate all of the page content. You should use a button in the tab instead. Also, there is an outstanding issue SPR#MKEE8P4L8D, the execId property on the xp:eventHandler tag will only work correctly when the target executed control is a NamingContainer, whose ID is included as a prefix in the ID of input controls in that area.]