Yes, as I said executing control definitions is not robust, and it seems trying to do that from an event is one way to prove that :-s
If you are willing to create an add-in instead, there you would have more options. E.g. there you could even cancel the save or close if not everything is as it should be in the drawing, then bring up a dialog listing the issues offering the user to fix them on the click of a button. Then you would be outside the event handler execution and probably it should all work.
Actually, the form part could be done in iLogic as well. So in one rule you could check the drawing (that is run from "before save" event) and if there are issues it would bring up a form which can run another rule that would do the actual work of changing the border.
In this example first the form pops up because "Mine" border is not used. Then user clicks "Fix them", the border is changed, and during the next save no form pops up, because all is fine:
http://www.screencast.com/t/sPoX2Vl6jvx
I don't think there is a way however to change the border before the document save takes place.
The real solution for you would be if AddBorder() functioned as it should, but not not sure when that will happen.
In the meantime I cannot think of a way to make the border change fully event driven, not requiring the user to explicitly run your rule (e.g. from an iLogic form).

Adam Nagy
Autodesk Platform Services