I have a number of Notes users who get an intermittant issue with Calendar invites and response items. When they open some invites or response items their Lotus Notes clients start to flicker and hang during the opening process. The only way to break out of this issue is to reboot the PC.
I believe the issue relates to user names in the various invitee fields and suspect it has something to do with the appending of the domain to each use.
Changing the tempate on the mail file has mixed results in resolving the issue.