Because I walk to work I tend not to use my car for days at a time. My previous two cars were Lotuses and I had the same issue with them with several different pad compounds and two different makes of brake discs (Elise Parts discs on the Elise, AP Racing 308 discs on the Europa S). And, like you, I'm now finding I also get the same on the Mito 155 depending on the weather. It can affect all sorts of cars
If you've got a garage or are parking somewhere secure that's flat then what can help is to leave the handbrake off but leave the car in gear (first or reverse) to stop it rolling (or even chock the wheels). Although if you do that make sure you remember to put the handbrake back on and take it out of gear before starting

. Leaving the handbrake off may not completely stop the problem though - with my Europa S it would still seize a bit when wet even with doing that (I'd also give the car a bit of a rock to and fro by hand just to loosen things a little, which would also help).