Direct3D 11 dropping to YUV420P on YUV444P content

Playing a x264 file in yuv444p through the Direct3D11 renderer results in yuv420p output. The other renderers (GDI etc) playback correctly.

This is using builds up to 3.0.5, Windows 10.

Debug info:

qt debug: Logical video size: 720x576
main debug: resized to 720x576
main debug: VoutDisplayEvent 'resize' 720x576
direct3d11 debug: picQuad position (0.00,0.00) 736.00x588.00
direct3d11 debug: Direct3D11 resources created
direct3d11 debug: Direct3D11 device adapter successfully initialized
direct3d11 debug: Direct3D11 Open Succeeded
main debug: using vout display module "direct3d11"
main debug: A filter to adapt decoder I444 to display NV12 is needed
main debug: looking for video converter module matching "any": 24 candidates
swscale debug: 720x576 (720x578) chroma: I444 -> 720x576 (720x578) chroma: NV12 with scaling using Bicubic (good quality)
main debug: using video converter module "swscale"
main debug: Filter 'Swscale' (000001e1fdf902d0) appended to chain
direct3d11 debug: D3D11 pool succeed with 1 surfaces (720x578) context 0x000001e1832b5248
main warning: Not enough display buffers in the pool, requested 3 got 1
main debug: original format sz 720x578, of (0,0), vsz 720x576, 4cc I444, sar 1:1, msk r0x0 g0x0 b0x0
main debug: removing module "freetype"
main debug: VoutDisplayEvent 'resize' 720x576