Sticky Piston And Redstone Block Bug

When I powered a stick piston to push a redstone block upwards, it worked, but when I unpowered the piston, it remained extended instead of pulling the redstone block back down. I tried this with a lever, a redstone torch and with some redstone dust between the power sounce and the piston and obtained the same result each time. It happened in both single player and online multi player.

However, when powering and unpowering a sticky piston with a redstone block facing downwards, everything worked as it should. When being unpowered, the piston pulled the redstone block back up.