Steps to reproduce:

1. Add an extra slash to the zabbix url: https://zabbix.example.org//
2. Navigate to Monitoring > Maps
3. Click on a map, e.g. https://zabbix.example.org//sysmap.php?sysmapid=11
4. Edit the map
5. Click update

Result:

Nothing happens, changes not saved.
**

Browser developer log shows an attempt to POST to https://sysmap.php/?output=ajax

Request fails due to CORS failure (good catch).

Expected:

Expected it to "just work", especially since everything else is working.  Guess the code that parses the URL is different on this particular page.