WARNING playername moved too quickly!

I am running a dedicated vanilla 1.6.1 server so that my friend over in America can connect and play along with me. The server is whitelisted, we're both in the list and have OP permissions. Playing creative mode.

We're building TNT cannons, some of which are designed to launch your player. We built one example which can launch a player over 700 blocks high - and my friend has no problem using this.

However, when I step in and launch myself, as the server host, it tells me that I am moving too quickly. My position is reset and I don't get launched in to the air. I have tried setting the allow-flight flag in the server properties file to true, but it still causes the warning to show.

Any ideas as to why I am affected, but my friend isn't?

Computer specs:

• Intel i5 3570k processor @ 4Ghz
• 8GB DDR3 @ 1500 Mhz
• Sandisk Pulse SSD
• NVIDIA GTX 670

Minecraft runs in windowed mode, but maximised.

My ping to the server is < 1ms (obviously), friend's ping is about 140ms.. Give or take 10ms.

My bukkit server still has the kick-on-speedhack parameter in the bukkit.yml file, but that might not be evidence of it being deprecated.

Add: kick-on-speedhack: false

under settings: anyway to give it a go if you haven't already.