Chances are what's happened is at the point when /dev/sdb1 was trying to mount at the usual location /media/idm/STORAGE-EXT the folder /media/idm/STORAGE-EXT already existed, so to prevent overmounting and hiding what's in that folder, the system mounted /dev/sdb1 under /media/idm/STORAGE-EXT1. This is normal, to protect the contents of /media/idm/STORAGE-EXT
In some instances, if you reboot, all will be fine, and you'll end up back where you started with /dev/sdb1 mounted under /media/idm/STORAGE-EXT.
However, in the meantime you (or a program) may have inadvertently added files to /media/idm/STORAGE-EXT while the disk is mounted under /media/idm/STORAGE-EXT1.
So the /media/idm/STORAGE-EXT will always continue to exist, and you'll persist with the disk mounting under /media/idm/STORAGE-EXT1.
However, if you check /media/idm/STORAGE-EXT and make sure it truly is empty with a simple ls -ltahr /media/idm/STORAGE-EXT then you can confidently remove the folder, reboot, and chances are it will all be back as it was.
If, however, there is data in /media/idm/STORAGE-EXT then you probably want to move/copy/delete it as appropriate, and the folder /media/idm/STORAGE-EXT then reboot.