pkgload::help appears to ignore help_type = "html"

[Kodiologist]

When I say devtools::load_all() and then help("foo", help_type = "html") to preview help on my function foo, I get text help, as with help("foo"). By contrast, help("sqrt", help_type = "html") works as expected.

I'm not using RStudio (or roxygen2), just plain R (and handwritten .Rd files). If there's a different way to see a preview of the HTML help for a function in an in-development package, let me know. I tried R CMD Rdconv -t html, and it works, but the output looks substantially different from what I see in R's built-in HTML help system. I'm not sure what's going on there.