Yes. A copy operation won't create a new keyword if the destination does not already have it.
To be more specific: each mailbox has a list of defined keywords used with that mailbox. New keywords are defined by setting a previously-unused keyword in a message while you have the mailbox open.
Appending new messages to the mailbox does not define new keywords, and it's not clear from the IMAP specification that it should. So if the source has a keyword that is not defined in the destination, that keyword is likely not to be copied.
-- Mark --
http://staff.washington.edu/mrc Science does not emerge from voting, party politics, or public debate. Si vis pacem, para bellum.
