Yikes.

I was close, so very close, to submitting my first paper, and then M had another look at the data.

M: Hm, maybe this is not what we thought it was.
Me: Huh. You may be right. But maybe what we initially said is right.
M: Okay. Well just to be sure, I need you to do like 10 more experiments.
Me: Uh, okay.
M: And also re-do the experiments that were going to go in the paper.
Me: @&%*$!!!

Now don't get me wrong -- I don't want to publish something if it isn't correct. And it's better to work these things out now, rather than have them brought to light by the reviewers (and thus risk having the paper rejected).
*But* the thing that bothers me is, I was ready to have this part done, out of the way, and possibly published, and now I have to wait even more. And it always takes longer to do things than you thought it would. I just don't want to have to wait another 6 months to get this out.

Crap. That's what I get for getting my hopes up.