[trunk] : Group by gives an error in Supplier and Customer list view.

Hello,

With latest trunk,

Go to Suppliers list view , either from Purchases menu or Accounting menu,
In its list view , try to group by Start Date or End Date, it gives an error:
"Uncaught Error: Grouping on field 'membership_start' is not possible because that field does not appear in the list view."

Same as go to Customers list view from Sales menu, try to group by Followup Level gives an error :
"Uncaught Error: Grouping on field 'latest_followup_level_id' is not possible because that field does not appear in the list view."

Thanks.
CGA.