CANCEL: Custom Action with OpenURL of form not working when triggered from Spreadsheet View - the form never displays

CANCEL: Custom Action with OpenURL of form not working when triggered from Spreadsheet View - the form never displays

This simple custom function works fine when triggered via Custom Action from a List view, via the Edit menu:
  1. void TSCG.new_lead_from_inquiry(Inquiry this_inquiry)
  2. {
  3.     openUrl("#Form:Lead" + "?Inquiry_ID=" + this_inquiry.ID, "Popup window", "height=550,width=900");
  4. }
(It simply opens our form to create a new Lead record, and passes a parameter.)

However, for a similar view of the same object, defied as Spreadsheet view, and a record is selected -- although the Custom Action choice does show in the header (the only place custom actions can show when in Sheet view), but when invoked, although the "Loading..." and "Please wait..." messages briefly appear (as expected and indicating that the form is preparing to display), the form never appears .  (And it is not somewhere else -a new browser tab or window).

Might this be a bug with the Spreadsheet view?  Maybe when using popup window?
Happens whether in Chrome or Firefox.
I'll be glad to demonstrate on phone and sharing screen.  Let me know.
Thanks...