render() versus Knit GUI for word_document - r-markdown

Question

I am trying to knit a table created by kable() and produce a Word document. When I knit using the RStudio knit button, it works fine and produces a formatted table. When I use render(), it does not. It produces just a unformatted string of text. Here is a minimal example:
test.Rmd
---
title: "Test"
output:
word_document:
keep_md: true
---
```{r pressure2, echo=FALSE}
knitr::kable(mtcars)
```
The render() command is
rmarkdown::render("test.Rmd", clean=FALSE)
The pandoc command that is run by both the Knit button (RStudio) and the render() command is
"C:/Program Files/RStudio/bin/pandoc/pandoc" +RTS -K512m -RTS test.utf8.md --to docx --from markdown+autolink_bare_uris+ascii_identifiers+tex_math_single_backslash --output test.docx --smart --highlight-style tango
I can see the problem in the test.utf8.md file produced by pandoc() when I run render(). The test.utf8.md file is an html table. I cannot see the test.utf8.md file produced by clicking the Knit button since that is not saved with keep_md=true. Only the test.md file is kept.

Answer 1

The RStudio Knit button must be changing the kable() format when output is word_document. If I change the kable() call to
knitr::kable(mtcars, format="markdown")
It works. The following sets the kable() format. I don't know what output format the user will select, so don't want to set format in the function call. Putting this with an if statement to detect if the output type is Word, fixes the problem.
options(knitr.table.format = 'markdown')