In certain situations TNT does not ignite another

I played in a map created in 7.6 and last updated in 8.0 build 7. I placed some TNT in my TNT catapult. Unexpectedly, all TNT except the one I ignited manually was not ignited by the explosion of the first one.
This applies not only in "Updated from a previous version" map but also occurs in maps created in 0.8