Here's what my content looks like, currently. Some of the columns are grayed off for some reason, and I can't change their visible/hidden/required status. It only happens with Integer columns. If I type in a manually crafted URL like /_layouts/ManageContentTypeField.aspx?...&Field=FieldName&Fid={GUID}, I can access those fields.
What would be the solution in this case, other than making those fields Number fields?
