I almost always launch mp3tag via a Windows context menu option. After installing the new release 3.19, I noticed that launching mp3tag via the context menu opened the prior version, 3.18.
Opening mp3tag from the installed desktop shortcut opens 3.19 as expected.
After installing 3.19, I found that I now I have 2 copies of mp3tag.exe.
I am sure I can fix my setup, but I assume this is unintended behavior for the installer. When installing 3.19 (and every other prior version) I simply accepted all the installer defaults.
The first one is the 32bit-Version of Mp3tag, the installer is called mp3tagv319setup.exe
The second one is the 64bit-Version of Mp3tag, the installer is called mp3tagv319-x64-setup.exe (or in your case was mp3tagv318-x64-setup.exe)
Could it be that you mixed them?
You can have a look in your (windows) control panel for installed software. I assume you will see two different entries?