Why are there double event signatures in the event list view?

Folks,

I am working on a 'monster' size window.  The srw is 1,153,382 bytes.

Look at the screen shot below. You can clearly see that standard events are double listed for the largest DataWindow Control in the event list view.  Custom events are not double listed.

Standard events are NOT double listed in the script editor drop down

This is the screenshot from version 12.6.  it is the same in version 12.5 and 12.1 (an earlier version of the same window).

Here's what I see.

The edit source looks as expected

I suspect something is amiss because when deploy as a 64 bit compile this window dies an unnatural death during load

I exported, changed the name in the source code and imported into another library.  Same result on the fresh object

How you ever seen any thing like this?