Rear brake seizure

To bed new engine in I experienced performance iSSueS if you wana call em that...this turned out to be a seized rear brake...whilst on a dual carriageway. I stopped realised the problem, but I couldnt move the bloody bike...so in the inside lane of the carriageway I stripped down the rear brake caliper, lubed, checked movement etc, and off I went. But just to make sure, I didnt use it again in fear of it happening again. I stripped it down again at home, nothing found. But still I havnt used it since the first seizure. Today, it started to seize up, just got it home. I repeat, I had not used it. Went out 30min later to find the problem...and it was free, no problem. Just zoomed up to me folks, free haircut and PC usage, and its fine Any ideas? Happend to anyone? Before you ask, yes it has had fluid changed, did it when first got the bike home.,id just get another caliper and see what its like,,,