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I had two classes:
gr=Class(db, "group", name = String(),
members=Multilink("user"))
gr.setkey("name")
Class(db, "order", name = String(), assignedto = Link("order"))

I developed it with back_bsddb3, and grouping on
"assignedto" property worked fine
("...&@group=assignedto..."). Then I switched roundup
instance to back_metakit, and grouping stopped working.

back_metakit seems to sort (since grouping in back_metakit
is done with sorting) items on "name" property.

If having two same properties in different linked classes,
then it's a bug. Otherwise it's not.