Redstone dust that turns a corner (and connects to something other than more dust) is either (a) failing to changing its shape when it powering things or (b) improperly powering things it shouldn't.

In the image, there are 3 setups of redstone dust "L" corners powering two redstone lamps. In each setup, there is air below the lamps and the inverted quartz stairs that support the redstone stuff. In each setup, different lamps receive power.

• The top left setup seems correct, the L does not reach to either lamp and neither receives power.
• The top right setup should display the redstone dust as a cross "+" or not power either lamp.
• The bottom setup should display a "├" (a T turned counterclockwise 90 degrees) or not power either lamp.