Boolean selector not working

[Sky-creates]

I have the following boolean property in my document:

---
Solved: true
---

However, when I want to select it in CSS, such as
node[Solved=true]{shape: rectangle;}
It does not work.

I have tried
node[Solved="true"]{shape: rectangle;}
node[Solved=True]{shape: rectangle;}
node[Solved="True"]{shape: rectangle;}
etc.

The only thing that works is
node[Solved]{shape: rectangle;}
However, this converts all node with property Solved to rectangles, which is not what I want.