This was mentioned in the Frndly Support thread and I am able to duplicate.
If you create a Custom Channels with the XMLTV URL filled in then later decide to try to completely remove the URL and leave it blank, the URL will come back and persist. The only way to remove the XML URL is to completely remove the Custom Channels source. Repeatable.
At first I thought this was part of the [Removal of Custom Channels Source Is Not A Complete/Full Removal] issue which was fixed. But it appears this is a different bug.