Blocks appears darker than expected with smooth lighting

Blocks looks darker when I place torches (appear with smooth lighting minimum and maximum, disapear with smooth lighting off)
Blocks look also darker even when there is no torches (and still with smooth lighting minimum and maximum)

Steps to Reproduce:
1. Mining down 1 block forward, 1 block under, like every players did
(1.2. Put torches on the upper block)
2. Light on the other upper block will appear darker