Adding names with _'s

Hi spigot,
So basically there's a admin on my server named _Dean[and then some more] and every-time I add him to the bungee config as an admin the bungee network just hangs and crashes until I remove him.
Now, I thought maybe it was just him, But I tried it with someone with 2x _'s at the front of their name and it still did it..

config:
groups:
danjb2000:
- admin
littlemonkeyleah:
- admin
Chris_122:
- admin
VxArctic_MinerxV:
- admin
Seppaman:
- admin


All I do is add:...

Adding names with _'s