I've noticed this problem a couple of times now. If a module is assigned to a menu item, and that menu item is subsequently deleted, the module appears on all pages. When looking at the Condition for the module assignment, the Menu Items section shows "0". It's quite surprising to make a change in the site menu, and suddenly have modules appears in places where you're not expecting them to appear.
But I cannot reproduce the issue with the module then showing on all pages.
Can you give me (super) admin and (s)ftp access so I can take a look?
And tell me on what url I can see/reproduce the issue.
You can use the 'Confidential information' button in the forum editor to hide sensitive information.