I've never had paint THAT thin that it'd actually flow around to the underside of a round part, unless it was totally unstirred. Are you STIRRING the paint? Shaking does nothing for acrylics--you can shake all day, and it'll still be 90% unmixed, even if the color looks right.
I'd suspect the cold garage at least partly---cold makes many things separate to the point that it takes MUCH more effort for them to mix again---they don't really mix, they just suspend themselves in much smaller particles, so they LOOK mixed, but aren't really.