Are you using any mods? Since you happened to mention a particular gametype it could be assumed that you do not have the same problem on other gametypes.
There are commands that stop map rotation in DM, in which case you just search for "tourn" in your config and will likely find one or two commands that could cause such an instance.
Map rotation is a common question so you probably found what you needed, but this post may not be in vain after all since other people with a problem may find that is related to rotation on gametype.