Explosion Lag

What I expected to happen was...:
TNT to explode after normal time when triggered/Creepers to explode normally when triggered

What actually happened was...:
TNT took several seconds to explode (in reproduction disappeared and then exploded) and Creepers (once triggered) would begin to explode, but at the final stage be frozen for a few seconds before exploding.

Steps to Reproduce:
1. Open Minecraft Java in snapshot Minecraft 18w43b
2. Place TNT/spawn a Creeper in creative mode
3. Trigger using a flint and steal (or in the case of TNT, redstone)