Please see T136792#2355255.
Steps to reproduce the issue:
- Semi-protect a page.
- Use another account that has no sysop rights.
- Using your secondary account (that has no sysop rights), move the semi-protected page to another page.
Both pages now have semi-protection, if you will see.
- Move the target page back to its source page.
At this point, you will see that only one page has semi-protection.
- Repeat steps 3 and 4.
Now you will see that the semi-protection is gone, without even using the unprotect special page.