To reproduce, set:

 hints_auto_exit_delay = 0;

This setting means you have to hit return to follow a link.

If you call the follow command, and type the number of a link, but
sneaky javascript deletes or hides the link before you hit return,
Conkeror still follows the link when you hit return.  The right
behavior would be to give an error that the link no longer exists.  If
we wanted to be sneaky right back, we could prompt the user to ask
whether to "force" clicking the link.  (though it's hard to imagine
when that would be useful)