HIVE

There is an oddity in how it saves where if you choose "MDX" file type, and you name the model "MyFile.mdl" in the save popup, then it will save the file to MyFile.mdx anyway. But if you manage to get it to save a file named MyFile.mdl while it is saving as "MDX", then it would not show that file you saved from within the Retera Model Studio when it is filtering only for files ending in ".mdx".

So, just to double check, what happens if you try these steps:
1.) Click on Peasant in unit browser to open default peasant model
2.) Click on File -> Save As and choose "Documents" folder.
3.) Save file as "Peasant.mdx"
4.) Open "Documents" folder NOT with Retera Model Studio, but with Windows Explorer
5.) Does Windows Explorer show the file "Peasant.mdx"?

I did as you askd, but Windows explorer doesn't show the Peasant file

If you have that folder open in Windows Explorer where the peasant file did not save, can you right click this folder and do "New -> Text Document (.txt)" and make a text file named "SimpleFile.txt" using Windows Explorer, or if you do that does the file disappear? (If it asks you to provide Administrator permission to save the file or something like that, then this is the problem because the Retera Model Studio does not have the Administrator permission. If that happens, you have to use a different folder.)