Uniform Buffer Object layout binding

[James A.]

I have two Uniform Blocks in my vertex shader :

layout(std140, binding=1) uniform Transforms
{
uniform mat4		mvp;
uniform mat4		proj;
uniform mat4		mv;
uniform mat4		nrmn;
}trans;

layout(std140, binding=3) uniform Shadows
{
uniform mat4 shadowMtx[2];
}sdw;

I can get the correct binding for Transforms using glGetActiveUniformBlockiv with GL_UNIFORM_BLOCK_BINDING but it gives me 0 for Shadows.

If I change Shadow to

layout(std140, binding=3) uniform Shadows
{
uniform mat4 dummy;
uniform mat4 shadowMtx[2];
}sdw;

querying GL_UNIFORM_BLOCK_BINDING now gives the correct location. Have I misunderstood something or is this a bug?

I'm using openGL 4.2 with Nvidia 460 w/ 296.10 drivers

Thanks,

James