Copy and Cut replace any data that the user may have previously copied to the system clipboard with the contents of the specified field. And this is not a necessary side effect as you can easily avoid it:
If [ IsEmpty ( Contacts::Street ) ]
Set Field [Contacts::Street ; Contacts::Postal_code ]
Set FIeld [Contacts::Postal_code ; "" ]
Go to Record/request/page [ next ; exit after last ]
Note for those new to scripting: When Setting up Set Field, there are two Specify buttons that must be clicked. To get Set Field [Table::Field ; Expression], add set field to your script and click the first button (specify target field). Select Table::Field from the list of fields. Do not click the specify button next to the repetition box. Click OK to close this dialog box. Now click the lower specify button (calculated result) and create the expression to the right of the semicolon (;). Do not try to type in the semicolon.
Thanks again :-)