I created a subfolder in the Program Files(x86) folder containing all files for a very old programme. (Jeff Parker's Alarm)
The data file, 'alarm.alm' was incorrectly associated with IE despite my attempt to select alarm.exe. Strange. At first I thought I must have made an error. Second try to correct this and the file was now associated with Photoshop. Crazy. There was no error. No way in Hades I had selected Photoshop! I tried again and it was associated with Notepad. Time to try something else.
I then moved the subfolder out of Program Files(x86) folder and into the root menu of the C drive and the problem disappeared . . . I was able to properly associate alarm.alm with alarm.exe and all is well.
Incidentally, this programme is not "installed" in a conventional sense. There is no install file. You just copy the files, including the exe file to the drive.
No idea why being able to properly associate a file should depend on its storage location. Is there something special about Program Files(x86)?