There is one thing you might check.
Are you using the same Automap file on all your computers.
If one block was set to insert for a different Layer in Automap then, this might be the answer.
If not you could send your Automap file to Glen.
Sorry Glen I have no time.
I had to do my Automap file all over again.
When I open a Old drawing any blocks that I have changed stay.
I have seen double blocks but only in old drawings that where used.