R markdown that has a problem with tmap_arrange..

gistfile1.txt

> packageVersion("tmap")
[1] ‘1.8’
> packageVersion("rmarkdown")
[1] ‘1.5’

tmap.rmd

---
output: 
  html_document:
   toc: true
---

Here's how I run this. Note my default graphics device isn't cairo-enabled, so the
first line is needed.

```
options(bitmapType="cairo")
library(rmarkdown)
render("fnord.Rmd","html_document")
```

If I haven't started a graphics device then the output HTML has the images in. If I *have*
started a graphics device, for example:

```
X11(type="cairo")
```

then the maps get drawn to that and don't appear in the HTML output.


```{r test}
library(tmap)
data(World)
w1 <- qtm(World, projection = "eck4", title="Eckert IV")
w2 <- qtm(World, projection = "merc", title="Mercator")
# tmap_mode("plot")
tmap_arrange(w1, w2)
# tmap_mode("plot")
```

Note that mucking with tmap_mode("plot") here and there modifies the behaviour in weird and unusual ways.