search pattern
  " ^libc6$ ?for x: ?depends( ?for y: ?depends( ?=x ) ) "
will match libc6,

but after bind() added, the pattern
  " ^libc6$ ?for x: ?depends( ?for y: ?y:depends( ?=x ) ) "
returns nothing.

And Example 2.3 & 2.5 on page "Search term reference" behave the same.
https://www.debian.org/doc/manuals/aptitude/ch02s04s05.en.html

I think there's a bug somewhere.