When setting the value for a sensor (Atmo Sensor, for example) or a building (Gas Flow Valve, for example), you must enter the value, then either right-click off of the item or press Enter. If you left-click off of the item before pressing return, the value you just entered will be lost and replaced with the last value successfully entered into that particular sensor or building.
For example, Lets say I create an Atmo Sensor, then enter the desired pressure (say 1000g) and press Enter (or right click) - this is a successful change. Then, I go to adjust another Atmo Sensor, but after entering the new value (say 2000g), I left-click something else, the value for the Atmo Sensor I was just trying to adjust will become the value I previously successfully entered (1000g, in this case), rather than reverting back to its previous value or taking 2000g as I typed.
I have confirmed this behavior affects all of the following sensors and buildings:
Gas Flow Valve
Liquid Flow Value
Gas Germ Sensor
Gas Temp Sensor
Liquid Germ Sensor
Liquid Temp Sensor
Personally, I would like the left-click to mimic the right-click, however reverting back to the previous value (effectively a cancel) would also be acceptable. Whichever you choose, it will be much better than changing it to an almost random value!
1) Create any sensor or building that has the option to set a numerical value for something.
2) Click on the sensor/building.
3) Enter an unusual value (1234, for example), or simply click in the entry box (do not press enter)
4) Left-click off the sensor/building
5) Click back on the sensor/building and observe the new value