Expected behavior: The join trigger can trigger when a downstream project is disabled

Actual behavior: It never does

Steps to reproduce:
1) Create three normal projects JobA, JobB, JobC that execute the attached simple batch scripts.
2) Create a project JobABC. Go to configure and
a) check "Build other projects" specifying JobA and JobB as downstream projects.
b) check "Join Trigger" specifying to run JobC when downstream projects are complete.
c) save
3) Build JobABC. Note that it runs JobA and JobB in parallel, then JobC when both are complete. This is expected.
4) Go to JobA's configure page and check "Disable Build" and save
5) Build JobABC again. This time JobB will correctly run... and JobA correctly does not run being disabled... but JobC will incorrectly never run because JoinAction is waiting for JobA's build result, which will never arrive.