Yes they are. Those same sensors are used in automotive MAF sensors and they have to work in a wide range of air intake temps that a car might see or you will throw an emissions fault check engine light.
Based on pure unadulterated speculation I am leaning towards a battery, capacitor or other chip (less likely) being affected by the cold.
Edit: Also the 0 MSL limit is crazy. It is very easy to get high pressure at close to sea level altitude to push the pressure above standard sea level pressure. If there is roll over or sign problem in the code this could be responsible for the strange failures.
I second your speculation that there is a temperature sensitive component other than the pressure sensor in the altimeter, or that there is a firmware programing error in the altimeter.
Most modern altimeters draw little power when recording data: most like the RRC2-mini and the MAWD draw 10 ma in normal operations. The issue is whether or not the altimeter will brown out when a pyro event is triggered.
An e-match is going to draw several amps when initiated, and if the uC is not brownout protected, the battery voltage will drop and uC may reset or go into an undefined state. (It is important to note that voltage is the critical factor for the uC, not current.) If the occurs both FETs might be switched on and the pyros activated or not depending on the available current. (It is important to note that current, not voltage determines if the e-match fires.)
This could be a battery issue. An 8-cell 9.6 volt NiMH transistor battery form-factor battery is probably not as good as a 6-cell 7.2 NiMH transistor battery form-factor battery which will supply more current because it has a lower impedence when used in a single battery altimeter configuration. Pyros fired at higher voltage draw more current and drop the battery voltage by a greater amount than those fired at a lower voltage, so the higher voltage, higher impedence battery being asked to supply more current than the lower voltage lower impedence battery whihch is never a good situation to be in. In cold weather you ideally want to use two batteries: one for the flight computer and a second for the pyros and the one for the pyros needs to be a low impedence battery.
Additionally I might have some concern about the temperature ratings of the capacitors and the chips. While most chips perform just fine below the minimum rated temperature, elecrolytic capacitors can have issues, particularly if they were ones manufactured after the capacitor plague of the late 90's.
Lastly it's always possible that there is a firmware error. No altimeter should be using absolute pressure alone to determine altitude AGL. The
pressure ratio of the pressure at altitude vs the pressure on the ground
can be modeled precisely with the US Atmosphere to yield altitude AGL, and the ratio should be used to avoid problems due to the +/-~6% atmospheric pressure variability due to weather on a given day.
Bob
