[luatex] tex.enableprimitives producing non-primitives?

[Élie Roux]

Hello,

this mininal example fails with   tex.enableprimitives('',
tex.extraprimitives()) in the (plain) format :

\directlua{tex.enableprimitives('testprefix', {'attribute'})}

\testprefixattribute 3 = 4

\pdfprimitive\attribute 4=5

\pdfprimitive\testprefixattribute 3 = 4

\end

it says "Missing primitive name on l7". Is it normal ? This behaviour
looks strange to me, as testprefixattribute should be a primitive...

Thank you!
-- 
Elie