I just tried it and what I found agrees with OP:
 
1. "H-Delay mono/stereo" always outputs a mono signal in Sonar whether it is inserted in a stereo channel or buss.
2. "H-delay stereo" works. I get good ping-pong on a mono track that has the interleave set to stereo.
It is also working as expected, in stereo, on a buss.
3. "H-Delay mono" works properly, It's mono and the H-Delay meter shows a mono channel.
 
Note:  The above scenario was tried with both the vst2 64 bit version and the vst3 64 bit version with identical results for both.
 
In conclusion: I agree that there is a bug with "H-Delay mono/stereo". Contact waves and notify them of bug.
 
The work-around is to just use the "H-Delay stereo" version. It works and does the desired ping-pong effect.
 
 

mikedocy
I just tried it and what I found agrees with OP:
 
1. "H-Delay mono/stereo" always outputs a mono signal in Sonar whether it is inserted in a stereo channel or buss.
2. "H-delay stereo" works. I get good ping-pong on a mono track that has the interleave set to stereo.
It is also working as expected, in stereo, on a buss.
3. "H-Delay mono" works properly, It's mono and the H-Delay meter shows a mono channel.
 
Note:  The above scenario was tried with both the vst2 64 bit version and the vst3 64 bit version with identical results for both.
 
In conclusion: I agree that there is a bug with "H-Delay mono/stereo". Contact waves and notify them of bug.
 
The work-around is to just use the "H-Delay stereo" version. It works and does the desired ping-pong effect.
 
 

Thanks for confirming mikedocy. I'll let Waves know there's a bug and will try the stereo/stereo version this morning.

Confirmed that the stereo / stereo instance works as expected. Thanks mikedocy!  I've contacted Waves and told them there's a conformed bug when used in Sonar anyway.  This is not a show stopper for me since the stereo / stereo instance works.  Will let you know if Waves gets back to me.
 
I must say that their customer service is excellent. They got back to me within a couple of hours and have been following up. 

I've had similar issues with Waves plugins (and others) though I do not have H Delay. I never thought of checking the stereo interleave so I'm going to do that tonight.
A work around I have come up with is two copy and paste the audio into two other tracks so you have three of the same track. Pan on left, one centre and one right. Load up the mono instance of the plugins on the L and R tracks and set to 100 per cent wet. Its probably not exactly the sort of sound you are looking for as it is not really 'true' stereo but it is a great way of faking a WDW rig for guitar and means you can very easily EQ the delay trails of either side etc.

In relation to my above post changing the interleave to stereo on a mono track fixed the issue for me with other plugins. Thanks all.