PSS A319 question concerning FMS

Hi!I am posting here because there was no response to this question in the PSS forum (2 days).When I make a change to the flight plan, such as a crossing restriction from ATC, then the destination i.e. KBOS just "goes away". That makes the selection of the "arrival" difficult. :) Attmepting to reload the flight plan just seems to create more problems.Are there known issues with flight plan changes? If so, I will operate around them. However, if it is pilot error, then I would like to know how to properly make the revisions. Thanks in Advance...BobP :)