Don't know of any differences in behavior for this trigger between v11 and v13. But portals are a little bit different. Perhaps you have a layout object, such as a field that is floating above the portal row instead of "owned" by the portal? (If it's owned by the portal, it will move when you move the portal while in layout mode.) If so, entering this field does not enter the portal and then the trigger would not be tripped.
Thanks. It moves with the portal. Just doesn't trigger. I've worked around it by using button set-up instead. If there are other things to try I'd like to hear 'em. Because it really is identical to the older database and it simply isn't triggering and that's just a bit maddening.
As a test, I took a file created with FileMaker 13 that happens to have a portal.
I selected the portal while in layout mode and used a right mouse click to specify that the onObjectEnter Trigger perform a simple script that uses a custom dialog to display the text "Hello".
In Browse mode, I can click into any field in the portal row or press tab while in the field that precedes the left most field in the portal row.
In both cases, the custom dialog appears as expected.