Breaking a spawner with silk touch gives you a spirit orb and the spawner, which can be placed and mined again for infinite orbs.

Bae the spawner doesn't drop anything even with silk touch. If it does, it's modded behavior.

Since it is not a default behavior, and detection of such occurrence is not really feasible without major workarounds, I won't be changing the behavior. Consider using spawnerSpritOrbDrops config value to disable drops fron spawners.