r - flexdashboard (storyboard: true) not working when runtime: shiny added

Question

I'm trying to use Rmarkdown, flexdashboard (with the option storyboard: true) and also shiny. Everything works fine until I add runtime: shiny. Then the frame tabs move faster than expected and even disappear.

I've tried two ways of specifying the storyboard mode, by adding storyboard: true (commented out in the example code below) to the YAML and by adding the {.storyboard} class to the page I want laid out as a storyboard. Same result.

You can see the different behaviour just by commenting in and out runtime: shiny in the code below.

Any ideas of what I'm missing? Thanks for your help.

---

title: "Title"
output: 
  flexdashboard::flex_dashboard:
    #storyboard: true
runtime: shiny
---

```{r setup, include=FALSE}
library(flexdashboard)
```


Analysis {.storyboard}
=========================================

### Frame 1
```{r}
```
***
Commentary for frame 1


### Frame 2
```{r}
```
***
Commentary for frame 2


### Frame 3
```{r}
```
***
Commentary for frame 3


### Frame 4
```{r}
```
***
Commentary for frame 4


### Frame 5
```{r}
```
***
Commentary for frame 5


### Frame 6
```{r}
```
***
Commentary for frame 6