Mark,
I believe this is a bug with VFP. And yes it is a royal PITA.
You can get around this by explictly clearing each of the classes you've defined in your application via the following statement.
CLEAR CLASSLIB [yourclass]
There's no way (short of CLEAR ALL) to clear all cached class definitions.
Pragmatically speaking, CLEAR ALL is probably the easiest workaround.
Malcolm