i think its normal, because when you shut down the engines, it will of course decrease the ITT but the Combustor chamber is still hotter than the ITT and will exchange heat, so the ITT will increase until a thermal balanced is set between the ITT and the chamber and it will then decrease toward the outside temperature.
I wouldn't be surprise that after shutting down the engines and power up the aircraft 45 min after, that the ITT will still be hot and increasing.
Next time, after shutting down the engine engines, display the engine temperature (TBM plugin menu), you will see that after a couple of minutes, the ITT will rise slowly until the temperature balanced is achieved with the combustor chamber.