Saving changes

I'm new to mp3tag and for now i'm using it for sorting out genre descriptions in my library.
I tried this: I opened a folder from my library clicking file - change directory. I selected all the files (mp3) that appeared, changed the 'genre' description on the left and clicked on the save button on the top left. The 'writing files' window popped up and when it finished all files seemed updated to the new genre.
However, when i right click on the files in windows explorer, click properties and details, the genre tag isn't updated.
Am I doing something wrong here?

You have to select all files in the files list that should get the same genre first, then set the genre and save it.

Thanks for your reply.
I don't know how's that different from what I did on my description.

look at your tools > options > tags >mpeg and see what tags you are reading and writing. Probably have both ID3v1 and ID3v2.3. In mp3tag you may be reading and editing ID3v2.3 and in explorer you may be reading ID3v1. (My preference is to delete the ID3v1 tag and only have a SINGLE tag in my mp3 files (ID3v2.3 UTF 16)

Many thanks garym! That solved my problem. I'll take your advise and keep just v.2.3.

All the best