Multi-line mathematics doesn't work correctly

[ellafm]

The first set of examples given in the help guide here are not rendered correctly (tested in Chrome, Edge)
https://mermaid.js.org/config/math.html

```{mermaid}
 graph LR
      A["$$x^2$$"] -->|"$$\sqrt{x+3}$$"| B("$$\frac{1}{2}$$")
      A -->|"$$\overbrace{a+b+c}^{\text{note}}$$"| C("$$\pi r^2$$")
      B --> D("$$x = \begin{cases} a &\text{if } b \\ c &\text{if } d \end{cases}$$")
      C --> E("$$x(t)=c_1\begin{bmatrix}-\cos{t}+\sin{t}\\ 2\cos{t} \end{bmatrix}e^{2t}$$")

```

Line breaks using <br/> also do not work when the text includes math expressions such as $$x^2$$

```{mermaid}
flowchart LR
  A["$$x^2$$"] --> B("$$x^2$$ <br/> Hello")
  B --> C{Decision}
  C --> D[Result one]
  C --> E[Result two]
```

[ellafm]

I've discovered that the first example can be addressed by replacing \\ with \\\ in maths expressions requiring newline characters.