By design: project's use of depth masking depends on strict objects rendering order. In this case the object rendering order is:
"Capsule","DepthMask",everything else.
Color buffer values withing the depth masked region are not initialized, because no other object passes ZTest, and the "Capsule" within is filling only a part of the masked area. So the remaining area within depth masked region remains uninitialized, and the values are undefined behaviour depending on GPU/drivers/devices.