Processing of `;%lwt`

I've stumbled across Lwt documentation which states the following:

With OCaml 4.04.0 and on a convenient syntax is available for sequencing Lwt operations using ;%lwt. This allows free mixing of standard ; sequencing and ;%lwt sequencing without extra parentheses

I've tired it, it did not work with Lwt as I expected, I've started an issue on that in Lwt repo and got the following input (by @hcarty):

Reason doesn't have proper ;%lwt support in its parser, so it ends up mis-applied to the surrounding code. So while ;%lwt works properly in OCaml code, it doesn't do what you'd expect in Reason.

Looks like this was not reported previously, hence this feature request issue. Is it possible to introduce proper support for monadic semicolons? Current behaviour when it seemingly works but does the wrong thing is quite counter-intuitive :)

Start by reproducing the reported ;%lwt behavior in the Reason parser and compare it with the documented OCaml behavior and the linked Lwt issue. No source file or test is named in the report, so the work is to determine the parser entry point, define correct monadic-semicolon behavior, and verify that surrounding sequencing is no longer mis-applied.