Yes I am very, very sure.
 
The problem is described here:
https://blog.lisk.io/lisks-holiday-security-reminder-44b49405384f

Cut and paste certain parts of the text out this page:

In the case of zero outgoing transactions from a Lisk account, the network only knows the Lisk address of an account, not its public key. This way in extremely rare instances, address collision is possible.

Therefore, it’s important to broadcast the correct public key to the network for any given Lisk address. This can be done by simply sending at least one transaction from a Lisk account.

The reason is; during the process of conducting one transaction from your account you have to use the passphrase, from which the private key and then the public key are derived. During that process the public key is also permanently cemented into the Lisk blockchain and associated with your Lisk address. This way even if a collision happens the network detects non-matching public keys, because a different private key will also lead to a different public key, and will refuse any outgoing transactions.

And this is exactly what happened to me.