NEC Univerge SV8100 Features And Specifications Manual page 196

Issue 8.01
When the following are done in sequence,

Call Forwarding Busy is set to extension

Call Forwarding Immediate is set on extension

Call Forwarding Immediate is cancelled on extension

then,
Call Forwarding Busy/No Answer is set back on the extension.
Default Setting
Enabled
System Availability
Terminals
All Terminals and Virtual Extensions
Required Component(s)
None
Related Features
Call Forwarding, Off-Premise
Call Forwarding with Follow Me
Call Forwarding/Do Not Disturb Override
Central Office Calls, Answering
Department Calling
Direct Station Selection (DSS) Console
Do Not Disturb
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UNIVERGE SV8100
Call Forwarding