Karlis is the Latvian form of
Charles and in my experience is usually a male name. The main Karlis I am familiar with is Dr. Karlis Osis, a Latvian-born parapsychologist:
http://www.llewellyn.com/bookstore/article.php?id=62
I can see how some American parents hearing or seeing the name could think of it as a feminine form for
Karl, however, as it seems to fit in with names like
Doris, Ardis, Corliss, etc.