Okay. I tested by hitting #, waiting for the dial-tone and dialing the number. During the dialing sequence, I can watch the numbers come up in the MJ interface just fine. However, again, once the call is connected, only about 40% of the time does the dialed number show up in the MJ interface.
For example, I was dialing a room code (say 123456), I would have to push each number 1-6 times before it would show up in the MJ interface. Once each number showed up, the conference call number recognized the correct room number. In other words, I had to dial "11112233344566#" for the conference call number to recognize "123456#".
Further testing shows the same problem happens with dialing out over Google Voice on SP1, though I can't watch exactly what numbers are actually recognized. Using the OBI test number (222-222-222), I can hear each DTMF tone as I press each number, but if I don't give sufficient time between each press, the tones won't play or they are cut off (a very short tone) or distorted.
With this new information in mind, I called back via MJ and found that if I left a 1.5-2 second delay between each number press, that the tone would get properly registered.
So it appears that the problem is that you cannot dial a numbers on a connected call without providing a full 2 second delay between each number. This is a fairly serious issue for anyone that uses their phone to call services that request information dialed via tones. A lot of support numbers request you enter your account number, last 4 SS#, telephone number, or other info on the phone. With this issue, I can never be 100% certain that anything I've dialed has actually been recognized as a valid entry by the recipient.