There was a bug in ANGLE's glUniformMatrix implementation as recently as version 963 that is fixed now. The bug was that a call to UniformMatrix4f with a count > 1 for a variable declared with, e.g., "uniform mat4 my_matrix[1];" would incorrectly cause GL_INVALID_OPERATION to be raised. Excess data is supposed to be ignored for arrays.
Is there now a conformance test for this? Since the problem has been fixed, I'm guessing there is.
Regards
-Mark