When you place a piece of redstone behind a piston then a torch at a diagonal, piston doesnt update until torch is removed and leaves block connected to piston behind.
Related issues
Attachments
Comments

[media][media][media][media][media]
The redstone dust must be pointing at the piston for it to activate. The dust does not automatically connect up, so the torch makes it go obliquely.
Duplicate of MC-1263.