There is normally some call progress supervisory signalling information passing back and forth commensurate with end-to-end call set up (which triggers ringing of the destination device) and simultaneously sending a call progress tone (NA Std. Ringback tone) to the calling party. By performing a quick release the Mitel does not recognize that a valid call was ever established. You might be able to tweak the trunk circuit descriptor assignment on the Mitel to get it to ignore supervision, but I don't even know if that's a valid (or settable) parameter for SIP trunks. The Mitel O/S referred to in that tech bulletin is fairly ancient code. Current shipping software for the (new 3rd gen) 3300 is now at release 11 (MCD-5.0) which isn't even supported on a box old enough to be running rev 7. As I recall Rev 9.x was the end of the line for the 2nd generation 3300's.
Mitel's web site still shows 7.x code as being supported, which usually means when you call with a stale issue that was addressed in later code they'll first want you to install the most recent S/W for the platform you have before working with you further. Of course without a current Software Assurance contract (Mitel's answer to Smartnet) you'll have to purchase the upgrade which could (depending on S/W level you're currently at) also encompass a hardware upgrade. TANSTAAFL (there ain't no such thing as a free lunch)
Original MUG/NAMU Charter Member