FYI - found a bug in Legacy.

Just for info. I submitted a trouble ticket recently that has now been confirmed as a bug and will be fixed in some future update.

Merging or deleting individual records that share events with others can cause a record not found error and could crash with a run-time error - and continue to crash on reopening. It doesn't necessarily occur when the recipient of a shared event is merged or deleted - but it does when it's the primary person. Temporarily un-sharing is a workaround. In any event - back up your data before merging or deleting in these cases - not just a merge backup, but a full database backup and it's useful to check/repair and compact after the merge or delete. This may not occur every time - but you could be caught with an unworkable database if you aren't careful.