If I remember correctly, I think the 2nd GSP that I trained kept sitting down when I gave him the whoa command. I thought it was odd but then I noticed that he liked to sit down at times while he was eating....I chalked it up to him just being lazy. LOL Anyways, I tried to cure it before it got out of hand. What I think I did (this was about 5 years ago so I'm not 100% sure about this) but when I was training him on a training table, I would give him the whoa command and watch his rearend VERY closely. If I detected the slightest bit of him trying to squat and sit I would flick his flanks hard with my finger and put my other arm under him to prop him up and then reposition his feet. I'm not positive if this is exactly what I did but it seems like something I would do to correct this problem. Whatever I did, he doesn't sit anymore so I guess it worked. Just watch him closely when giving the whoa command and be creative with your techniqes....every dog responds differently. Hope this helps!

How old is your pup? Have you tried putting him on some planted birds and then giving the whoa command? If he's birdy enough and intense while on birds, then maybe he'll forget that he wants to sit. I dunno....just a thought.