1 {du'u2 ce'u broda} = x1 is the property of being broda
2 {du'u2 ce'u broda ce'u} = x1 is the broda relation
3 {du'u1 ce'u broda} = {du'u ma kau broda}
= x1 is a (true) completion to {du'u2 ce'u broda}
I conclude that {du'u1} and {du'u2} should be expressible by different
cmavo. {du'u1} is the one that deviates from current Lojban, so
would call for an experimental cmavo ({du'au}, say), if only in order
to allow for a lexicosyntactic form that is closer to logical form.
So how about when ce'u and qkau combine? E.g.
4 mi se cfila loi du'u ce'u prami ma kau
"Who I love is a flaw in me"
5 {mi se cfila loi du'au ce'u goi ko'a zo'u jetnu
fa lo'e du'u ce'u prami ko'a}