ADV7511 works with SPDIF audio in 480p 60Hz but not 576p 50Hz video modes

We are using the ADV7511 to provide HDMI video+audio for a computing device. 

This works fine for 480p 60Hz and for 576p 50Hz, if we have no audio. 

However, if we enable the SPDIF audio (at any sample rate), then the 576p 50Hz video mode stops working, i.e., the monitor acts as though there is no signal.

This does not occur if we are using the 480p 60Hz video mode.

ADV7511 I2C main map register values:

:00:140031001000000000001D8E00180113
:10:2537200000F03000466204A800001C00
:20:1CBF04A81E70021E000004A808121BAC
:30:00000000000000000000008011114400
:40:C010707E7970000010A8800004000000
:50:0000020D001219000000000000000000
:60:00000000000000000000000000000000
:70:010A0001000000000000000000000000
:80:00000000000000000000000000000000
:90:00000000C00024800302E01830611100
:A0:0000A4A4080400000000004000004002
:B0:00000000000000000000000000000000
:C0:00000000009006004202000002000104
:D0:3CFF8080800000000000000000001001
:E0:D0780000600000000000000000000000
:F0:0000000000751100000000005D000156

Is this a known errata, or is there something Bleeding Obvious that we haven't got right?

Any suggestions of leads to follow up would be most appreciated.

Paul.