Version:           1.5.5 (using KDE KDE 3.5.5)
Installed from:    Fedora RPMs

I opened umbrello and selected Diagram -> New -> Entity Relationship diagram. Next I created an (empty) entity, run the code generation wizard and it generated code and saved the file. (language was sql)
Then umbrello was closed and later I reopend the file, added some more entities and executed the code generation wizard again. Only this time only the entity I created before reloading the project was there.
I also added to each entity an attribute after that and ran the wizard again (on only the first entity) and looked at the output file. It contained exactly the same code (empty create statment) as the first time. I tried deleting the generated file but this gives the same result.

After I created a new file with the same properties and created 2 entities, now the code generation wizard show no classes at all.