DUna,
I am happy to explain the situation to you. There are two different temperature probes in the Triad that are used to take report the shelf temperature as well as two different ways to cool the shelves.
In the pre-freeze mode, the shelves are cooled by refrigerant from the compressor that travels through the shelf. This allows the very cold -70C temperature to be reached. There is a probe in the refrigerant for the shelf giving a true reading of the shelf.
There is also a temperature probe located in the Lexsol line (heat transfer solution that runs though self that can be heated or cooled for precision). In normal operation mode (not pre freeze) the shelf is cooled by the Lexsol that runs through the shelves not the refrigerant and the temperature is read from the temperature sensor in the solution. Normally there is a transition period when the shelves enter normal operation and the Lexsol is chilled to match the shelf temperature and then it takes over the temperature control of the shelf. Because you hit Run/Stop without going through the transition phase, you simply jumped from reading one probe to reading the other probe. In the scenario you gave us, the shelf would have still been very cold as they cannot go from -70 to -28 in a few seconds. Because you put it into normal mode by hitting the run/stop button, the reading was coming from the probe in the Lexsol.
I hope this makes sense to you. Let me know if you have any other questions.