My english is bad. I apologize for my bad english.

I've been watching tutorials and learning on my own too, but I cannot seem to be able to find a solution to this problem in particular, or maybe I simply don't know how to describe it. :(

Context

I am rigging a large dragon model for a game. When it comes to the tail bones, I have 3 bones making his tail and they have the limit rotation constraint, but the bones seem to ignore the constraint.

When I'm testing the Y-axis rotation limit, instead of going up and down, it makes a kind of an "S" shape slide. Funny and weird, because the bone seems to be entirely ignoring the restriction to not rotate over the X-axis.

This animation will clarify what I mean:

Summary: when I test Rotation on Y-Axis on the tail, first up/down, then it goes to right/left. The tail moves in an "S" shape even though the X-axis is limited to 0:0. I honestly don't know much about rotation engines or measures like Euler or quaternion, I haven't messed with that yet.

I attached a .blend file for further comprehension of my issue.

EDIT

Thanks for the elegant edit of this post, forgot to link the .blend file

https://drive.google.com/file/d/14nmny0wEqOcibfAlXmsPhZO7ZNUYfxFa/view