Irrlicht Engine

Any ideas left?

In your example you can change the order of multiplications and it works the same way. Your arbitrarily assumed order left-to-right, but this is not cast into stone. Matrices are usually* applied right to left.
No I can't change the order, because quaternion-multiplications are not commutative ...

There is a project that aims to provide a LUA-binding to Irrlicht:
http://irrlua.sourceforge.net/

LUA is a very popular scripting engine and is used in several big projects (like WoW).

But man, that is really a n00b-question (for an advanced problem).

I agree with the op, imho it is implemented wrong.

a *= b shoul mean a = a * b and it is implemented as a = b * a

That will not work if you want to add a rotation to another one.

E.g.:
If you want to rotate you object over each axis, you may do something like this:

// Non-rotation unit ...