It is possible to start an Mp3 for playing.
(Right click and 'Play' in the open context menu, or doubleclick onto the title)
Now there is no button to stop the sound !!
When I repeat the step then MPlayer opens (same song or a different)
It should open the first time.
I had a look at the problem you're describing and it seems that it's related to the way Mp3tag opens the file. When Mp3tag opens a file, it sends a message to Windows that states, that the player window should not be activated and the player should be opened in minimised mode.
Unfortunately, WMP interprets this in a very special way and displays no window at all. It's definitely not a bug and I'm not sure how a change of the way Mp3tag opens files for playing would affect usage habits of other users.
Thank you very much, Florian.
I tried later versions.
Version 2.39 works fine for me.
In version 2.40 'my' problem occurs the first time and in version 2.41 it still persists.
It would be appreciated when other users can confirm 'my' problem.