MXMLC incremental not working on OSX

Question

I'm working on an Apache Flex project that used to be developed on Windows and is now being developed on OSX. Back when we were on Windows, we fought and fought with MXMLC and its incremental command line option to avoid recompiling unchanged files. In the ended we ended up having to use the raw-metadata option with an empty string to ensure the metadata was consistent so the .cache check would match and files wouldn't be recompiled.

Yesterday, however, I had to move the project over to a Mac and now MXMLC is producing new files every time. I can run the command back to back on the same file without touching anything else and a new file is being produced. Whats weird is that I am not getting the typical debug message Failed to match the compile target, the cache will not be reused and yet it recompiles the swf and makes a new cache file anyway.

I've read in other posts on SO about the flex-config.xml file in the Apache SDK being updated with a new modified timestamp and that causing the issue, however I'm monitoring the file and the modified date is not changing at all.

I'm wondering if anyone has experienced anything like this? BTW this is Apache Flex 4.9.1 on OSX Yosemite.

The command I'm running is...

/Applications/Adobe Flash Builder 4.7/sdks/4.9.1/bin/mxmlc -optimize=true -incremental=true -debug=false -raw-metadata '' -output target.swf input.css

For what it's worth, I've tried with toggling both optimize and debug differently with the same results. I've also tried removing everything except incremental and it still produces a new file with new checksum every time I run the command. I'm at a loss.