Strange Encryption Bug

We are currently migrating databases from MySQL to
Postgres SQL when we noticed a weird bug in MySQL.  It
only happened once but it was strange enough to catch
our attention.  I�m very much a newbie when it comes
to databases so I can�t really diagnose errors or bugs
that well.  Anyway, for security purposes we encrypted
the ID numbers of our users in a user table.  Whenever
a transaction from that user comes in, we record the
transaction in a history table where we copy the
corresponding user ID in the history table.

For example the original user ID from the user table
is �12345abcde�.  Now the user ID that we see in the
history table became something like �12345fghijk�.

We were only able to track the specific record since
we have a time stamp and another field number given by
a secondary server that verifies the transaction.

I�m not really quite sure why this happened.  This is
the first time the bug happened with MySQL.  Any
theories why the error existed?  Can this also happen
when we migrate to Postgres SQL?

Thanks in advance!

Regards,
Joanne


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