It was quite amusing until a friend filled the village we live in with decorative azaleas. I have a feeling it's because maybe azaleas are grouped in with plants such as tall grass and flowers, mobs consider all these non-solid?
I can confirm for 1.18. What I found interesting when I saw the bug is that the zombie did not jump on the nearby moss block either. I will put a screenshot of what I am talking about on this report.
Code analysis (Mojang mappings, 1.19.2): This is somewhat tentative, but I believe this is what is happening: AzaleaBlock extends BushBlock; BushBlock#isPathfindable(...) calls BlockBehaviour#isPathfindable(...), which returns true (for the land and air path computation type) if it doesn't have a full block collision. Azalea blocks don't have a full block collision (they have a custom collision box), so it returns true. As such, mobs think they can pathfind through them.
The easiest fix would be to create an isPathfindable(...) method in AzaleaBlock that overrides it to always return false:
Can confirm. Could be intentional.