Metal fragment shader receives incorrect interpolated vertex z values - objective-c

Question

I have a simple vertex shader that outputs position and color and a fragment shader that outputs color. There is also depth testing enabled with a texture that I created.
struct VertexOut {
float4 v_vertex [[position]];
float4 v_color;
float4 vsVertex;
};
vertex VertexOut vertexShader(uint vertexID [[ vertex_id ]],
const device RigidFormatPos* vertices [[ buffer(0) ]],
const device StdVertexData* vertexData [[ buffer(1) ]],
constant SettingsUBO& sceneUniforms [[ buffer(2) ]],
constant MeshUBO& perMesh [[ buffer(3) ]]) {
VertexOut out;
out.v_vertex = sceneUniforms.cameras[0].projectFromWorld * perMesh.worldFromModel * float4(vertices[vertexID].pos.xyz, 1.0);
out.v_color = float4(float3(vertexData[vertexID].color.rgb, 1.f));
out.vsVertex = out.v_vertex;
return out;
}
fragment half4 fragmentShader(VertexOut in [[stage_in]]) {
return half4(half3(in.v_color.rgb), 1.f);
}
The screen dimensions are 800x600.
Xcode debugger shows the value of in.v_vertex.z = ~857.3434 while it has to be in the range [0,1] after the divide by w. The value of in.vsVertex which is in clip space that I have manually cached and output from the vertex shader shows correct z value that after divide by w would be in the range [0,1].
This causes depth test to fail.
Has anyone encountered anything like this. Any ideas on where to look next?
If I manually output depth values to the depth buffer using depth = in.vsVertex.z / in.vsVertex.w depth test works as expected.
I am rendering to a CAMetalDrawable render target color attachement, using a depth texture that I created.