pfSense

well that is very weird. I opened chrome and tested, it worked correctly. I switched to a firefox tab, selected DHCP leases and got the same artifact (incorrect operation) reloaded, and it worked correctly. I restarted firefox between the first and second test.

Definitely cannot be reliably replicated even on my system. I'll make sure to screen grab the hover if I see it again.

Have you defined DHCP pools?
Do the effected entries have DHCP addresses issued from the pool(s)?
I can see that the code in status_dhcp_leases.php that calculates which interface each IP address comes from, is not going to work with IP addresses that have come from a pool.

Yes, they are all fine. If I hover over the plus button for more than a few MSEC, the URL fills out completely and then I get the correct and expected result.

I suspect this is ultimately neither particularly important nor particularly easy to fix. I have a pretty large DHCP pool attached to a tiny little logic supply fanless computer. I doubt there is enough delay in a more appropriately balanced system to permit catching the link before it is fully constructed. It is more likely to be merely interesting that it is possible to do so than a real bug.

So I don't know what your bug is - that is really weird if the link has "if=" with no interface, but then the interface value comes after a while - e.g. "if=lan".
There is a bug if you have multiple DHCP pools. The interface corresponding to IP addresses in the extra pools are not resolved back to the interface they are in, and that makes it go wrong in the way it is in your screen shots.
This should fix it:
https://github.com/pfsense/pfsense/pull/1631