Hi,
When using two #forminput elements with parameter "popup" on a form page that uses HeaderTabs, the first popup doesn't work on the first tab. It does work on subsequent tabs or outside the HeaderTabs. I suppose it's some JavaScript getting in each others way.
Best regards,
Frank
MediaWiki 1.27.4, Header Tabs 1.1 (2b61294) 01:27, 5 May 2016