First of all: I know this kind of bug has been reported many times. This looks like it but it's a bit different.

I've noticed myself that rotation within a summon command doesn't work. This is quite annoying if you're trying to summon mobs with NoAI , since they're always pointing south in default. This is also confirmed by many other bug reports. The way to solve this is to use a teleport command to change to rotation.

 /tp @e[] ~ ~ ~ ~90 ~

for example to rotate your entity 90 degrees. This works fine.
Until you relog.

What I expected to happen was:
the mobs (in my case the villagers) would stand in their original position I put them in.

What actually happened was:
the mobs (in my case the villagers) were again pointing south, the default setting.

Steps to reproduce:
1.Take a command block and place it down.
2.Summon an entity with the tag

3.You'll see it's pointing south
4.Use the teleport command I mentioned before.

 /tp @e[] ~ ~ ~ ~90 ~

5.You'll see that works.
6.Close your world
7.Open your world
8.You'll notice the mob pointing south again

Screenshots
1. Before relogging
2. After relogging