Erratic From addresses

[MWE]

I am running Outlook2000 under WinXP. I have a half dozen
profiles (A, B, C, D, E and F); each profile is for a
different email account. Each profile has a separate and
distinct Internet Email service and a unique pst file,
e.g., A.pst or B.pst. Each profile also is "connected" to
several common pst files, e.g., Com1.pst and Com2.pst and
common a address book. Some profiles are also connected
to the unique pst files of other profiles, e.g., A is
connected to A.pst and B.pst. I have the option turned on
that automatically places a copy of each outgoing message
into the Sent Items folder.

The following has occurred more than once:

I am in, say, Profile A and send some email. After
connecting to the relevant server and flushing the OutBox,
I check the Sent Items. The items that should have been
sent are all there BUT some of them have the wrong From
address, i.e., they have a From address from another
profile. There is some consistency to what happens, e.g.,
if in A and the wrong From is used, the From is always
from, say, B and never from C or D or E etc. If the pst
file held information on the From address for that
account, I could understand the confusion. But that
information is held in the Internet Email service "file"
and there is only one such file connected to any profile.

Any ideas what might be happening here?

Thanks