Yes it is!
Only sign in a device,
But there are as SDS extension to another device backup!
BLF KEY but all in the same set of equipment!
The current situation, for example:
Extension 2000 press KEY 1, 1000 can ring extension,
But in 1000 the extension is busy,
2000 does not show the extension KEY1 busy indication (LED not lit)!
Also occurred before,
We need to remove the extension and re-establish this extension to exclude abnormal!
I do not know there are easier ways to have excluded this situation it?