I don't know if anybody is interested in this problem, but if so here is an update.

Corel Support's suggestions have not solved my problem, so today I created my own test tone video.  I put a different tone into each of the 6 channels in sequence and used the panner to position them in turn in each of the six speakers. In the video I display a changing picture showing which speaker should be playing the tone at any one time.  When I play the video back while in the Timeline, the little blue dot in the panner icon positions itself in turn in each of the correct speaker positions.  As I only have two speakers on my laptop I can't tell if the actual sound is in the correct position, but all channels play in turn out of at least one of the speakers.


So I then burned this to a BD using the PCM 5.1 surround setting and checked the resulting BDMV folder on the disc with MediaInfo - it showed 6 channels of PCM.  When I play the BD back through my amplifier the result is still the same - front, centre and LFE channels work correctly, tone for Left Rear speaker comes out of Right Rear Speaker, tone for Right Rear Speaker is silent.  When I use this video to create an mp4 file, PS24 uses 5.1 Dolby Digital surround sound and the file plays back perfectly through my amplifier.

As I only have one amplifier capable of playing LPCM I cannot confirm that the fault is not in the amplifier decoding process, so I have raised a ticket with Denon and await to hear from them.  Nevertheless, when I play the BD back on my laptop, the missing channel is apparent, so there is a problem somewhere on the disc.

This is why I would be most grateful if someone else could make a Blu-ray disc in PS24 using the 5.1 PCM and tell me if it plays back perfectly on their sound system.