The issue:

Redstone torch doesn't power the piston underneath the block that is underneath the torch itself.

What was expected:

The piston extends when gets placed next to the block that is powered by the redstone torch.

The following screenshot explains the problem with the piston placed in different places next to the powered block(as it was supposed to be) 

Update: The versions were affected by this bug are from 0.16 beta to the current version.