You're very welcome! I try to watch for opportunities to contribute to the community by acting as a "bridge" between the forum and GitHub. Sometimes there is valuable feedback in forum posts that would otherwise be missed by the Arduino developers.
Generally I would prefer to narrow down the cause of the bug more so the developers can jump straight to fixing it but there's a lot going on in FastLED, I'm not very familiar with the new arduino-preprocessor, and it's a busy time of year for my business. I'll be interested to see what the culprit is.
I'd like to urge any interested parties to take a little time to do some testing of the beta IDE build. If you remember what happened after the introduction of arduino-builder in Arduino IDE 1.6.6 you'll understand why it's much better for us to find these bugs before they get out in a production release. The Arduino developers tried to make an extra effort this time around to get beta testers but I haven't seen a lot of reports about the beta build. That may be a sign that there aren't a lot of problems or maybe people just aren't using it. I've been slacking on it so this was a good reminder.
It's a bit strange that they push the new code out to the Arduino Web Editor since that seems like it's more targeted to beginners.