I'm not surprised. When I called about ours a few months ago, I asked if I should just wait, since the vouchers don't come until right before the trip, and the girl told me not to wait, because the prices can (ans sometimes do) change rapidly, especially with peak season approaching.
I would presume the jump you see is due to summer, and the fact that LMT.com was new to DL, and trying to get a niche in the market, which now seems to be happening.
5 day parkhoppers are normally $249, so it's still a savings, but if I were you, I'd go with DL's site, which has a special right now for 5 days for 3 at $184 per ticket.