Another option would be to try a Right-Click (or Control-Click) and
choose the “Download Linked File” or “Download Linked File As…”
option. That will download the file without trying to open or unzip it.
I ran into this trouble yesterday as well with a zipped extension (a zip file with an .mdx file inside).
It appears that if a module or extension has .zip an extension, OS X’s default decompression utility will unzip the file, then automatically unzip any zip files it finds inside (that is, any mod and extensions).
It all happens pretty fast, and what you wind up with is the Images folder, the Build File, and other stuff, exactly as the thread describes. Confusing for a newcomer to Vassal, who wouldn’t recognize this as the guts of a module.
StuffIt Expander seems to not do this–only the original zip file is unzipped.
I hope there is some elegant solution to this that also addresses the issue IE7 users downloading the modules from certain sites have where the browser grabs the MIME type, often incorrect, instead of using file extension information, leading to a similar and related though not exactly the same conundrum.
It all seems to be more or less the same problem to me.