asterisk users - Aug 2005 - Ast.1.0.9 (only) strange problem with IAX and DDNS

Asterisk 1.0.9: IAX2 registration timeout!
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I have 2 locations with ADSL lines, both with dynamic IP (+ dynamic
DNS).

On location 1 => Asterisk 1.0.RC2 / Slackware 10
On location 2 => Asterisk 1.0.9 / Slackware 10

They are on private network and connected via IAX2 through
NAT(win2000server), and registering to DDNS name of each other.

I know that Asterisk is not very smart on handling DNS, so when remote
ADSL change IP address, I must reload IAX on local Asterisk to (resolve
new address and) continue registering itself to remote Asterisk.

But, here start problem:
Asterisk 1.0.9 (location 2), sometimes (very often) when LOCAL ip
address is changed, can't anymore register himself to remote Asterisk
1.0.RC2 which by the way DIDN'T change it's IP address! Remote Asterisk
(unchanged IP) also can't register himself to local Asterisk (changed
IP) even when I do "reload" of IAX (on remote Asterisk). That problem
cannot be resolved with unload/load IAX2, or stop/start Asterisk. Only
reboot of local Slackware (location 2, unchanged IP, Asterisk 1.0.9)
helping, and after reboot everything working well (till some of next IP
address changing).

There things gets interesting:
Asterisk 1.0.RC2 (location 1) didn't had that problem. Then, 2 day ago,
I upgraded  to 1.0.9, and now I have same problem on BOTH location!
Registration to other networks (FWD for example) working with no
problems, only registration to each-other is impossible.

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here is configuration:

LOCATION 1:

[general]
register => L1o:[L1]@location2.ddns.address
[L2o]
type=peer
username=L1i
auth=rsa
outkey=L1
host=dynamic
qualify=yes
canreinvite=yes
disallow=all
allow=ilbc
trunk=no
[L2i]
type=user
username=L2i
auth=rsa
inkeys=L2
qualify=yes
context=incoming
canreinvite=yes
disallow=gsm
trunk=no

LOCATION 2:
[general]
register => L2o:[L2]@location1.ddns.address
[L1o]
type=peer
host=dynamic
username=L2i
auth=rsa
outkey=L2
qualify=yes
canreinvite=yes
trunk=no
[L1i]
username=L1i
type=user
auth=rsa
inkeys=L1
context=incoming
qualify=yes
canreinvite=yes
trunk=no