Matrices in shaders (ViewProjection vs manual input)

Hey all

Was having an issue today with making a shadow map

the shadow map generator was using the PROJECTION (e.g. tP) to lookup the depth value of each pixel

But when I was checking the depth value later on (to perform the shadow), i was using a custom flaot4x4 input without semantics (e.g. tProjector).

I found that the values didn’t match up.
After a bit of searching I found that the matrices were different depending on how they were fed into the shader

i was finding that matrix element 2,2 was 1.001 on 1 input, and 1.000 on the other, both with the same transform connected.
Very strange!
There were of course no other transforms connected that could have caused this disparity

My presumption is that something is happening down the PROJECTION line that changes the transforms a little.
Anybody any idea what it is?

it even works fine with tV : VIEW
only tP gets affected it seems
perhaps something to do with near/far planes?