The issue is as follows:

1) The customer adds article A to an eZ Flow block ( a manual one for instance )
2) The object is publied, and Article A is made visible by the cron
3) The object is edited again, and Article B replaces Article A
4) After the cron has been executed, Article B is published, and Article B is part of the history
5) The customer tries to edit the object, and attempts to remove Article B, and make Article A active again.
6) The object is published, but Article A remains in the history, and isn't made visible.

in point 4) I think the second sentence should start with "and Article A".