Tcsh command history

This is probably something everyone knows except me.

When I am not using X, Tcsh maintains it's command history normally.

When I am using X, my commands appear to written to the .history file. If I leave X and start it again without logging out, the commands will still be there.

But if I logout and then login again, all the commands I used from within X are purged from the .history file, leaving only the commands I used before or after X. Is there any way to stop it (tcsh?) from doing that?