OK I tested this across all major moodle versions, and it does exist in ALL major moodle releases. Here is how to reproduce:
1. Create a wiki page, then click on th e"Update this wiki" button
2. Make sure that you change the "Allow binary files" pull down menu from to "Yes" (for moodle 1.7 and 1.8 you might have to click on "Show Advanced" first). Click on "Save changes"
3. Then click on the "Edit" tab, here you will see the "Browse" and "Upload" button (see screenshot)
4. If you accidentally click on the "Upload" button without selecting any file, moodle will give you a blank page and you can't even go back to previous page - you are forced to close this window... very confusing for users
There should be at least some kind of error / warning message and allow users to retry again...
I could probably come up with a fix later and post it here.