I have not seen this behavior, so I will chalk it up to something else
causing it.

1) Do you have any security related software (antivirus, antispam, personal
firewall) installed that could be causing this?  For example, it is not a
good idea to let antivirus software perform real-time scans on the PST file.

2) Review personal firewall (ZoneAlarm, Norton, not Windows Firewall) and
make sure that Outlook is permitted communicate outbound as well as inbound.
If you every patch Office/Outlook, double check this configuration since all
products that I'm aware create a signature for that file.  Patching changes
that signature and the security software might not adjust or prompt you
about the change.

Outside of that in regards to subject line.  Double check your settings in
Internet Explorer.  If the option is set to use a dialup account, then this
could cause some interesting behavior when you have a broadband and dialup
access available to you. (I always leave my laptop set to never dial a
connection.   This way programs like antivirus or outlook can't trigger a
dialup session and will always use whatever type of connection I already
have.)