I have set up a list with two content types. When I click the New Item button, a dropdown is displayed which contains the two content types. So far so good. However, the forms behind those buttons are incorrect: in both forms, only the columns from the default content type are shown. If I check the urls of the 2 forms, I can see that the correct content type id is in the querystring. But still, the contents of the form are incorrect.
Any ideas?
If you didn't create custom forms for those content types, the problem is definitely not in forms. The problem is in the fields.
But I am not sure which fields - list fields, content type fields, content type fieldlinks, web fields.
First, look at list fields. Check their presence on list settings page and wheather they got right content type names in the column on the right and give us that information.
Are the fields in the form the incorrect fields or is it that fields are missing? If they are just missing you can try check the field properties in the content type and in the list definition schema to make sure the ShowInNewForm, ShowInEditForm and ShowInDisplayForm properties are correctly set to true. Another thing you can try, assuming it is not being deployed through a web template, is to export the site with sharepoint designer, import the wsp in visual studio and examine the content types and the list schema
