existing scala file in vim, then :Envim causes omnifunc to be unset

[megaannum]

If I start vim with no file, then launch envim (:Envim), and then load a
scala file (:e some/scala/file.scala) then omnifunc is set correctly:
:set omnifunc
returns envim#Completions

If, on the other hand, I start vim with a scala file,
vim some/scala/file.scala
if I execute
:set omnifunc
returns envim#Completions
as expected. But if I then launch envim (:Envim), and then check if omnifunc
is set:
:set omnifunc
returns omnifunc=