File extension . being changed to _ when downloading in IE 9
I am setting up a new standalone Win 7 64-bit laptop in school. It was running IE 10 but I uninstalled that by removing the update. Now running IE 9.
The issue is that when I try to download anything through IE, it fails the first time and at the second attempt (clicking Retry) it downloads the file and changes the file extension so that instead of being .exe or .pdf, it becomes _exe or _pdf. IE is also failing to open a pdf when I choose open instead of save - no error message, it just does nothing. I can deal with the file extension change by just renaming it, but my users are going to get confused!
I've done the setup on other Win 7 64-bit laptops, and they have been fine. This is the first one I've had to roll back to IE 9, and the first one to behave like this. I've tried Googling the issue with no success. I am guessing there is a setting somewhere that is set too high, but no idea where to look.