Please help! HP05s and xp12a motor cutting out - HeliFreak

Hi, I have a big problem at the moment. I sold a brushless mcpx with the following set to someone on here:

- Asteroid designs Dual MCPx Inline / fin
- XP-12A 1-3S ESC
- HPO5s brushless motor
- The steve BC
- Micro deans connectors
- Hyperion 550mah 1s batteries

The issue is that when he goes to spool it up with a linear throttle curve the motor cuts out! I don't understand why this is happening as I am pretty sure I have spooled it up with a linear throttle curve before. But The way I usually spool up my mcpxs is:

1. Flip Throttle hold on
2. Flip idle up 80% or 100% flat throttle curve
3. Move throttle to mid stick
4. Flip off throttle hold.
5. Fly

I have never experienced this motor cut out using this method, but it doesn't seem right that the motor cuts out with a linear throttle curve. Is there a setting on the xp12a you have to set up that only effects a linear curve?

I really don't understand and it's really bothering me and the buyer. So do you guys have any ideas?