[NTG-context] many "unknown reference" with the beta

With ConTeXt beta I get a lot of messages like

references : unknown reference [][fnt:f:1] references : unknown reference [][fnt:t:2] references : unknown reference [][fnt:f:2]

and sometimes referring to a reallabel

references : unknown reference [][discrete:wave]

What do these imply? I do not get them when using ConTeXt stable. G