I may not be following fully, but are you just wanting a generic description for the part to be guaranteed to show in the explorer column?
If so, the @ configuration is the one that drives everything. It looks like you probably typed the ".Default" yourself. Use the @ configuration on the data card and this will drive the description logic for what appears.
Hope that helps, sorry if that isn't 100% what you meant.
I may not be following you fully as well but, in a model, the last description you edited (custom or configuration specific) will be the one that shows up in the description column in the vault.
I'll be damned you're right. I've never noticed this. Well, that's a default. The way you can change this is in the Columns in the Admin Tool. You can set the variable to be read from a specific configuration. This can be @, or Default, or whatever.
Note: This option does not seem to be available for the Search Columns.