You found a bug! We've classified it as
We encourage you to continue the discussion and to find an acceptable workaround while we work on a permanent fix.
Thanks for your help on providing info for us. I was finally able to reproduce the stack overflow issue, and that one is fixed in the upcoming 2.2 release.
I haven't been able to reproduce the other "could not find master instance" issue, but we have done some work in 2.2 that should hopefully prevent you from getting in that situation.
If after the 2.2 release you still see this sort of issue, please let us know so we can circle back around on this.
Sencha Architect Development Team