Unfortunately we're not being that clever here, this just looks like a small bug with our UI.
We added the Min/Max/Value/Step value for Slider Widgets so if someone had a slider that with, for example, a range of values 0 to 1000, and all they cared about was increments of 10, then they could set a 'step' of 10 so they could hit numbers like 480, 490, 500, 510 easily with a mouse without getting values like "489.55".
That's all good in the context of a Slider Widget, but it seems to have bled into the Slider control we use for setting the temperature of the trigger that you've asked about. It doesn't make sense here since you're creating the trigger then moving away from it -- you just need the slider and/or the 'value' box so you could type a value in (really just the 'value' box).
The idea about allowing for some fluctuation so you don't have the trigger firing every time the temp changes between 74.99 and 75.01 is a good idea though, and something we should implement as an option in the future.