Strange behavior updating secondary dns.

[GiuseppeV]

Hello,
I've Plesk 11.09 (migrated from 9.x).
everything works fine except for updating the secondary DNS server (configured as slave, run bind).
IP address of plesk primary server is 10.100.10.110. Ip address of secondary DNS is 10.100.10.100.

For most domain update of primary dns work fine and notify secondary DNS, I can see:
Log from plesk server:
Oct 2 19:56:38 techsystem named[18846]: zone name.it/IN: sending notifies (serial 2012100208)
Oct 2 19:56:38 techsystem named[18846]: client 10.100.10.100#57599: transfer of 'name.it/IN': AXFR-style IXFR started
Oct 2 19:56:38 techsystem named[18846]: client 10.100.10.100#57599: transfer of 'name.it/IN': AXFR-style IXFR ended

Log from slave DNS:
02-Oct-2012 19:56:36.294 notify: info: client 10.100.10.1#21750: received notify for zone 'name.it'
02-Oct-2012 19:56:36.294 general: debug 1: queue_soa_query: zone name.it/IN: enter
02-Oct-2012 19:56:36.294 general: debug 1: soa_query: zone name.it/IN: enter
02-Oct-2012 19:56:36.295 general: debug 1: refresh_callback: zone name.it/IN: enter
02-Oct-2012 19:56:36.295 general: debug 1: refresh_callback: zone name.it/IN: serial: new 2012100208, old 2012100207
02-Oct-2012 19:56:36.295 general: debug 1: queue_xfrin: zone name.it/IN: enter
02-Oct-2012 19:56:36.295 general: info: zone name.it/IN: Transfer started.
02-Oct-2012 19:56:36.295 general: debug 1: zone name.it/IN: requesting IXFR from 10.100.10.110#53
02-Oct-2012 19:56:36.295 xfer-in: info: transfer of 'name.it/IN' from 10.100.10.110#53: connected using 10.100.10.100#57599
02-Oct-2012 19:56:36.296 database: debug 1: calling free_rbtdb(name.it)
02-Oct-2012 19:56:36.296 database: debug 1: done free_rbtdb(name.it)
02-Oct-2012 19:56:36.296 general: debug 1: zone name.it/IN: zone transfer finished: success



For some domain this procedure does not work.
Log from plesk server:
Oct 2 19:57:26 techsystem named[18846]: zone name2.it/IN: sending notifies (serial 1349200646)
Oct 2 19:57:27 techsystem named[18846]: client 10.100.10.1#27198: received notify for zone 'name2.it'

In the secondary DNS server there is'nt any connection.

As you can see the notify was send to 10.100.10.1 and not to 10.100.10.100.

I tried to delete and recreate the domain in plesk panel; switch dns master off / on ; restore default dns setting...
but nothing works.

Any help will be appreciated.
thank you!