pistons are not visible

If you move sticky piston with block (the piston is facing up) with another sticky piston (on image 1) the piston is not visible , but if we give near the diapered piston the piston apper.

What I expected to happen was...:
the pistons are visible /Picture twoú

What actually happened was...:
look at Picture one (this wos only once and after this i tesed it on the same thing but it did not happen)

Steps to Reproduce:
look ad top of the issue