Why not use IDLE? Workbench is a lot of code and dependencies.

I expect that it works because idle.app was created using the --no-zipimport option that is new in 2.7.

However with zip import the code is badly broken.

Build IDLE.app with zip import and you should reproduce the bug.

Have you code inspected the module as I suggested to review the new code?

_getSiteCode is clearly wrong. The if is backwards and no else.

The following inserts are in the wrong order:

if %(optimize)s:
    sys.argv.insert(1, '-O')

sys.argv.insert(1, mainprogram)