I have noticed the occasional use of a postverbal morpheme ka (with low tone) in my recordings of the 1990s. Some speakers use both COP and ka. (I do not have enough data to make generalizations —linguistic and sociolinguistic —about its occurrence.) The earliest examples come from vinyl recordings of dance music (probably the 1970s). Perhaps ka has been adopted from Lingala or Kituba, because a lot of this music was created, it seems, by musicians in Brazzaville.
Source: Samarin 2001: 136