Plesk 12.x / Linux :: Missing Resellers On Migration

We have a problem migrating from 11.0.9 to a different server running 12.0.18. Our Plesk 11 server is running great since years ago. We have 3 resellers there, say reseller1 with 17 domains, reseller2 with 13 domains and reseller3 with 250 domains.

First, we executed a complete server migration with:
/usr/local/psa/bin/migrate -m -host xxx.xxx.xxx.xxx -password xxxxxx -ip-mapping /root/migration-mapping.txt -skip-license -replace-existing-objects true

The process ran properly, but in the end we've found reseller1 and reseller2 were NOT migrated. No errors were reported tho.

While investigating this issue we have found:

1) "/usr/local/psa/bin/migrate --list-resellers" returns only reseller3. So it looks like reseller1 and reseller2 are not "seen" by the migrate utility.

2) /usr/local/psa/bin/migrate -mr reseller1 returns:
Migration started at: 2015-06-03 04:21:11
The following clients not exist: reseller1

3) /usr/local/psa/bin/migrate --list-subscriptions returns the 250 subscriptions of reseller3, but no single mention to reseller1 and reseller2 subscriptions.

In short, reseller1 and reseller2 are invisible for the migration utility. Both missing resellers are ok, enabled and active in our Plesk 11 server.

We are now stuck on the migration process and wondering if this could be a bug in the migrate utility? or some inconsistence in our Plesk 11?