Exported module doesn't show up unless unzipped

I exported a module, then manually edited the client.xml to add some reference data. While I have that module unzipped to a folder, it shows up for selection in the library normally and all of the contents and reference data are available as expected within the campaign. If I zip the folder and rename it back to a .mod file, however, it is no longer available for selection.

If I unzip it to a folder again, it functions as expected, so it doesn't seem like it could be corrupted, but can anyone offer an explanation for why it only works when I have it unzipped to a folder? (I'm using 7zip, if that could be an issue...)

Sounds like one of two things:
1) You're not using ZIP compression.
2) You're zipping up from outside of the module directory - ZIP from within the module directory so that the data files are at the root of the ZIP file.

Yep, #2 was the issue. Doh!