This was reported internally by @okiehsch, and
cause was pinpointed by @gwarser.

The issue could cause redirection rules to be
ignored under some circumstances. The repro steps
were:

- Navigate `https://adblockplus.org`

Result: A delay before the page renders.

Expected: No delay before the page renders,
because uBO is supposed to redirect to a local
neutered version of `googletagmanager.com/gtm.js`.