the title is in a \vtop and not a \vbox, and its height is fixed to \strutht (and the depth to \strutdp)
so basically the title is one line.
OK, I’ll do my best to stick to one line.
I guess it would be better to use a paragraphs or column environment for long labels but the ConTeXt is generated by pandoc, which writes 'definition lists' as \startdescription \stopdescription.