[chromehorse]

Given that this seems to only happen in the winter, and i am assuming that the rear brakes have been serviced and all pivots and adjusters are working fine, i would suspect that there is moisture in your parking brake cables. Overnight, you apply your parking brake and the moisture freezes. The ice would hold your cables in place once your handle is released, hence the "loose" feeling handle. Once the cables heat up from the exhaust, or just slowly slip (since ice wouldn't be able to hold it forever) the cable would release. A similiar cause would be if someone tried to lube the cables at some point and used improper grease and it is "freezing/thickening" with the same results as if it were moisture.

Hope this helps.