Trial spawners cannot spawn silverfish at all/have unusually long delays between spawns

Trial spawners with silverfish can not spawn them at all or have unusually long delays between spawns.

How to reproduce:

1. Place down a trial spawner and use a silverfish spawn egg on it
2. While standing on top of the trial spawner, switch into survival mode (if not already in it)

Observed result:
The silverfish don't spawn at all.

Expected result:
The silverfish spawn as usual.