Posting this for posterity and the benefit of others. I started typing this response, but then discovered the truth.
(Original thinking)
Sorry, but that does not sound correct to me.
I run a dual delay with stereo feedback into a Reverb and it doesn't collapse to mono. I hear distinct left and right delay repeats.
Further, levipeto said it sounds like the Reverb and Delay are in parallel, not that he cannot hear the delay...
(After researching)
However, I just checked the Reverb block diagram in the manual... And I think understand (and you are correct).
I think the "wet" portion of the Reverb is in fact collapsed to mono, but rest of the signal (the dry) is in stereo. This explains why in sounds as if the Delay is in parallel with the phase reverse enabled.