We are upgrading to AEM 6.5 from AEM 6.3 - I am facing an issue with Dropdowns and DatePicker fields in custom tabs page properties[Touch UI]. I think this is not the issue with the any fields. Each Item is setting into fixed columns and when we try to open DatePicker or DropDown - Window is shrinking and show like below even though - we have more space on the window. I tried to build a new custom tab looking at the documentation - Still I am facing the same issue - I don't what has changed in AEM 6.5 on this - I see some depricated folders in foundation (granite/ui/components/coral/foundation/form/fieldset)
Repository Restructuring occurred since AEM 6.4 onwards. So, when you upgraded from AEM 6.3 to AEM 6.5, all the OOTB stuff moved to new locations, whereas the custom one didn't. Due to that, you maybe running into such issue.