qiskit: H gate does not get decomposed correctly

Information

• Qiskit Terra version: latest (0.26)
• Python version:
• Operating system:

What is the current behavior?

An H gate does not get decomposed correctly. It is easy to see this at optimization level 0:

becomes

when it should involve no more than one sx gate and two rz gates.

Steps to reproduce the problem

What is the expected behavior?

An H gate gets decomposed into the correct minimal set of basis gates.

Suggested solutions

It looks like the decomposition for s and sdg does not know they are simple z-axis rotations.