I get test failures:

automation.c:2545: Test failed: Expected ERROR_SUCCESS, got 2
automation.c:2550: Test failed: Expected ERROR_SUCCESS, got 6
automation.c:2551: Test failed: Expected imaname, got H�2
automation.c:2556: Test failed: Expected ERROR_FILE_NOT_FOUND, got 6
automation.c:2561: Test failed: Expected ERROR_SUCCESS, got 6
automation.c:2562: Test failed: Expected 314, got 0
automation.c:2567: Test failed: Expected ERROR_SUCCESS, got 6
automation.c:2568: Test failed: Expected imaname, got H�2
automation.c:2573: Test failed: Expected ERROR_SUCCESS, got 2
Makefile:227: recipe for target 'automation.ok' failed
make: *** [automation.ok] Error 9

This is the kind of patch that could use lots of tests, though it
looks like you are working on it ;-) It would also be a good idea
to check a few real installers, such as those for .NET and Office,
if you haven't done so already.

If you have the disk space, running winetricks-test invokes a lot of real world installers and is pretty good about finding the occasional MSI regression.

Ping me on IRC if you need help with that.