Merlin switch-to-ml/i not recognizing current module

I’m trying to use Merlin to jump between .ml and .mli files from Emacs. It seems like Merlin does not detect the current file I’m in and open the corresponding .ml[i] file. When I run the merlin-switch-to-ml function, I get a prompt saying Module: [No match] and I have to manually type in the module name. By comparison, using tuareg-find-alternate-file does the right thing and moves me to the correct file. Am I misunderstanding the Merlin functions, or is Merlin doing something wrong?