Initial testing with 1.8.8.0 appears to be promising on my end. I created a new RRD and schedule, and it worked with no errors. My next legacy RRD/schedule doesn't fire until 12:45 (4.5 hrs from now) so I'll know when I get back from lunch whether the fix appears to be solid across the board.
UPDATE: The legacy schedules ran without a hitch. Looks like we're okay in 1.8.8. Now I just need to make sure Inline HTML is working, which is why we were waiting so eagerly for 1.7 in the first place.
UPDATE: Yep, the Inline HTML works too. Happy!