WowAce

What does the provided patch do?

If latency bar has "embed" enabled, it will break the cast bar if you cast a spell that does not send a UNIT_SPELLCAST_SENT, such as tilling a patch of soil at your Halfhill market farm in Pandaria.
Reproducible just by mounting or whatever, and then trying to till.

Patch nils out sendTime after using it. I'm not familiar enough with Quartz though so I don't know if this is the right way to fix it, but at least the bug that's been bugging me (heh) for a while now is easily reproducible

I have tried to reproduce this with the instructions you gave and using the patch you gave. I have not seen anything I'd deem out of the ordinary. Can you describe (or better: show in a screenshot) what goes wrong?

Tilling while mounting is not allowed, by the way, so I've used mounting, a casted heal, and a channeled AoE - both without and with your patch (no difference). Version 3.1.1 was used for testing this.

I have the same issue.

Here's a screenshot showing a good castbar: http://i.imgur.com/eMpH3.jpg

Then I leave the "vehicle" (the vine), mount, then click the vine again.

Here's what happens: http://i.imgur.com/bJkTX.jpg

It looks as though the cast is cancelled, though it's not. This happens on vines, when tilling, on the Amber Shaper fight while in a construct, etc.

Reloadui fixes it, but as soon as you mount 1 time it's broken again.

I've been trying to find a fix to the problem for a long time. I believe the issue only occurs when using Quartz in combination with Dominoes and or Pitbull. I've read several posts describing a conflict between Quartz and Dominoes/Pitbull for the player cast bar.

Unchecking the embed option within the Quartz latency settings has resolved my issue while tilling and on the vine. Haven't tested yet but I'm going to assume it will fix my Amber-Shaper vehicle cast issue too.

Sorry I can't provide more specific information but perhaps this will help to better describe the bug. OP are you using either Dominoes or Pitbull in combination with Quartz when you were seeing this issue?