Why amanda creates incremental dumps to holding disk?

Hi all

Amanda-2.5.2p1 on both the server and client.
The backup devices are vtapes on the server.

I ran amdump on the server.
The backup would be "full dump (Lv0)".
After I ran amdump, I found the vtape directory not being correctly set.

I Thought that the backup was failure.
When I checked the log($logdir/DailySet1/log.yyyymmddhhmmss), I found that the amanda creates incremental dumps.

----
ERROR taper no-tape [No writable valid tape found]
WARNING taper changer problem: Virtual-tape directory /var/vtapes does not exist.
FINISH planner date 20080123192410 time 1.344
SUCCESS dumper ctamanda /var/test 20080123192410 1 [sec 0.455 kb 10 kps 22.0 orig-kb 10]
SUCCESS chunker ctamanda /var/test 20080123192410 1 [sec 0.219 kb 10 kps 191.1]
STATS driver estimate ctamanda /var/test 20080123192410 1 [sec 1 nkb 42 ckb 64 kps 10]
----

Would you please answer to my questions follow whether if they are possible or not?

1) Why amanda creates incremental dumps to holding disk?
Amanda is supposed to redirect the dumps to a holding disk in the follow case:
- No tape drive.
- The cable became disconnected.
Why amanda doesn't fail backup and creates incremental dumps to holding disk?

2) Do you judge that which module is it?
Do you know whether to judge that which module is "Lv1"?
Planner? Driver?

3) Why amanda-2.5.0p2 isn't creates incremental dumps to holding disk?
Neither this time nor the same thing didn't intermited though did by amanda-2.5.0p2 (amanda2.5.0p2-4) that the bundle was done with RHEL5.
Why amanda-2.5.0p2 isn't creates incremental dumps to holding disk?

Your prompt reply would be greatly appreciated.

Takashi