Reversing the order has the same effect as transposing the matrix:

(A.B)^{T}=B^{T}.A^{T}

GLM has the same behaviour as GLSL: matrix*vector treats the vector as a column vector, vector*matrix treats it as a row vector (i.e. it's implicitly transposed to make the multiplication valid).

Indeed:
changes:

Code :

_vector = _trans * _vector;

The result is the same:
vec4(-5.311184, 5.000000, 4.877635, 1.000000)
vec4(-5.311184, 5.000000, 4.877635, 1.000000)