Hi Patrick,
The documentation and blogs which are available for Solutions are at very high level (good of sales folks, doesn't help devs :)). I hope CRM 2011 Solutions team will release more information about how each Solution component behaves under
different solution layers and configurations. Its bit of a mystery currently.
Problems like yours may be investigated by looking at the DB tables. Few tables whose peek between your imports may clear some of the mystery are
dbo.SolutionBase - solution layers are stored here
dbo.SolutionComponentBase - relate with layers and see if your components
MetadataSchema.ManagedProperty - relate iscustomizable and other metadata properties with your attributes and see the behavior
Manny Grewal || Australia