charm() and data.table not compatible?

[Paw1173]

Hello, I seem to run into a problem when using data.table structures in a html markdown document and then encrypting it with charm(). Encrypting it directly with output: fidelius::html_password_protected works for the same content.
Example 1 (direct method, no error):

title: Fidelius and Data.table Test
output: fidelius::html_password_protected

library(data.table)
cars.DT <- as.data.table(cars)
summary(cars.DT[dist > 30, dist])

Example 2 (file test.Rmd):

title: Fidelius and Data.table Test
output: html_document

library(data.table)
cars.DT <- as.data.table(cars)
summary(cars.DT[dist > 30, dist])

When I then run charm(test.Rmd), I get an error message
"Error in x[j]:
! invalid subscript type 'closure'"

Any ideas what causes this behaviour? Thanks.

[Paw1173]

Apologies, copying in the code lead to some of it being used for formatting the post. All code and headers were in .Rmd files.