Hi Glenn,
You didn't do anything wrong.
To explain the reason, I need to make it clear how do we (or the system) distinguish different airframes. Manufacturer, model and construction number are counted in, nothing else. So seats, engine number, etc doesn't matter.
The reason is, before Glenn's linking action, aircraft N5190Q was linked to airframe ID 380303, while aircraft 139990 was linked to airframe ID 621656. Why? Because the c/n are different, one is "139990" (please note this is c/n, not same as aircraft 139990, which is tail number), and the other is "unknown". Glenn's linking action will insert another aircraft record, whose tail number is N5190Q and link to airframe ID 621656 (the one aircraft 139990 use). So now we have two N5190Q, pointing to two different airframes.
I will manually fix it, by removing airframe ID 380303 and coresponding aircraft record. In the future some functions may be created and open to selected members to provide an interface so they can fix the problem.
I hope I explained it clear enough. It IS a bit complicated.
Ken