As I said I have a simple test stack that works the way I would expect it to. Therefore of no value at all.
I have no problem sending you the project I am working on. I can instruct how to demonstrate the problem, which is simple and straightforward, but I would not wish trying to dig into the guts of the thing on anyone.
Assuming it is not some edge case bug in LC, I do not know if my issue is of general interest to anyone but me, Currently I pre-open the substack but keep it hidden until the handler that is actually intended to open it runs. I mentioned that the fact the subStack is already open allows the mainStack process to proceed normally.
If anything, that workaround makes me think it is not something I did, but rather something in LC itself.
I do not really have confidence in that last statement.

Craig