Well, when you start your patrol and the patrol order screen comes up and begins typing out your orders, you'll notice that the orders come from "BdU/SUBPAC". During the patrol, you'll also get contact information and other messages and they all come from "BdU/SUBPAC".
It's just an annoyance, but it's a big annoyance (the Yanks are reading ADM Doenitz's mail!). The other comment was just a joke; I don't really think that aforementioned annoyance is the cause, but my last couple of careers were ended swiftly and unceremoniously by "Hunter Killer" groups that I ran into just as I was entering my assigned patrol area. Seemed like they knew I was coming and were waiting for me.
Since I haven't played OM in quite awhile and am trying to fix the OP ship ID problem before starting a new career, I can't remember right off-hand what other little annoyances there are, besides the message headers and the ONI recognition manual. But, there are a few others that seem to stem from SH4 being a USN Pacific Fleet sim to begin with.
As for the Capt's Log date issue, I remember seeing a lot of discussion on that, but don't recall that any "fix" was ever developed.