I had a similar experience when moving data into a modified structure, so I had a rethink and have since used the ALTER TABLE syntax. Works fine.
You need some code that has a look to see if the structure is what you want, if not run the ALTER TABLE stuff.

>When deploying new database structures of applications that are already in use by our customers, we want to upgrade the dbc and the accompaning dbf structures, without erasing their live data.
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>We tried to by making an empty copy of our own developer's database, moving the customer's data in a backup dir, placing our empty (new) one in the data directory and with an "append from" statement to add the live data into the new structure (added fields will then be left blank; that's not a problem).
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>The problem is that during the data-import the stored procedures are triggered and cause multiple errors, ending in a complete mess....
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>We're eager to hear other people's experiences and possible third-party products that make it possible to 'weave' an old (data-carrying) database with a new (empty) one.