Control add-in inconsistency

Hi all,

I've been messing around with control add-ins for years now and it still amazes me how many times I get stuck getting them to work in NAV.
This is the current situation:

A page in a NAV 2016 dev system. It has a control add-in (JS) field for a file drop zone. Everything works fine.
I export the page and import it into a clean NAV 2015. Everything still works fine and even compiles in 2015.

I then create a new page (50000, Addin Test). Create a new field on it and select the same control add-in from the list.
Now the trouble starts. It does not add event handlers for the 2 events that are in the add-in. But the events are visible in code in the original page in the 2015 system.

The add-in is registered correctly in the Control add-ins page in the RTC with all the same values as in 2016.
The javascript resources have been imported. And of course, it works fine in the RTC on the original page.

Original (with the events):


New page (without events):


The add-in itself could not be simpler...:


I know for a fact that the dll containing the add-in is present in the 2015 services because I see it in the 'Server' tab when I create a dotnet variable. It even lists all the types:


Any suggestions? Have I been doing something wrong all these years or is this whole add-in business still bugged as hell?

Gr, Erik