Can't add 3rd divisi - bug?

I have a situation where I already have a solo and altri line (strings), and am trying to add a 2nd solo line, but nothing happens. Also, when I bring up the Change Divisi dialog, it shows only “unis.” even though there is already another line. Have tried this all over the score, and the problem remains. Is this a bug?

Here’s the Dorico file (with the notes removed)…
string divisi issue.dorico (3.2 MB)

Seems to work OK.
All I did was double click the Divisi signpost and add the second solo!
string divisi issue-edit.dorico (1.5 MB)
(Or have I misunderstood?)

Oh!! Double click the signpost… somehow I hadn’t thought of that :rofl:
Thank you!