Some
J2EE containers, JBoss included, have options to do just this to your CMP tables on a table-by-table basis. While it seems odd that only one of your tables wuold be set up this way, it does seem likely to be the cause. Scan your JBoss-specific deployment descriptors for a setting like "create-table" or something similar.
I've never used JBoss, so I don't know the name, but
XDoclet has settings for just this behavior (create, alter and remove tables).