Redstone dust doesn't appear on a side of a block & piston

Redstone dust don't appear on the side of:

1. A side of a block when a piston above the dust, however, it seems like the redstone dust under the piston gets signal when activated like normal, so it's only a graphical problem.

(But when I replace the piston with an observer, it works as intended and the redstone dust underneath shown on the side of the block. You can see an example of how it is should be in the picture named 'works as intended').

2. On a side of a piston.