[PyrNet-L] At wit's end

Sam (almost 4 mos) was doing so well! (Note the past tense here)......... lately, when we put him outside to do *his thing*.... he's out there at least 1/2 hr usually, and when he comes inside, he does it in the house! He gets told *OUTSIDE* and put back out, stays there at the door as if to say *what'd I do?*? And comes back in after a period of time, just to do it again! And we repeat the whole process all over again. I have praised him, treated him etc when he does it outside.... scolded him ....and thrown him out when caught in the act inside- when he is caught in the act, he KNOWS he is wrong and stops mid-stream or mid-poop (now there's a feat!) and looks guilty... gets tossed OUTSIDE and does not continue to do his business. I am at a loss, (and running out of newspaper).... I just don't get it. He doesn't do a thing when we are walking, or in the car, or upstairs or in the bedrooms....... I have cleaned the carpets to get the odor out, thinking that maybe he thinks that that's the potty place by odor...... any suggestions? We DO start puppy obedience classes on Wed.....