3D Signal Undetected

Recently upgraded my receiver to a 4k compatible Sony STR DN-1080. Since setting up this receiver 3D signals are no longer detected by my TV. I have a large 3D library which i watch on my Windows HTPC. Even when i change the Intel resolution to 1080p, the DN-1080 still doesn't recognise it via the video 2 HDMI in, flashing the resolution up as 3840 x 2160. How can i get the receiver to see the HTPC as the 1080p source?, which will therefore allow 3D passthrough. The receiver upscaling is turned off.