Dera Sam,

"Behind That Curtain" was not included because that film was not a part of the Charlie Chan series proper. That is, yes, it was based on a Charlie Chan novel by Earl Derr Biggers, but, as you have seen if you have seen this film, Mr. Chan, played very haltingly by E.L. Park, appears only at the very end of the picture and for only about five minutes total. As was the case in the early efforts to put Mr. Biggers' Chan stories on the big screen, the tales bore only a surface resemblance to the original stories, whith Charlie Chan himself relegated to a minor role.

I hope that this quick explanation helps. In my humble opinion the right decision was made in not including "Behind That Curtain" in the box set DVD collections. Perhaps it could turn up as an "extra" in some future release, but it would only be as something of a footnote in Charlie Chan lore and history.

Sincerely,
Rush

Behind that Curtain is a fairly reliable cure for insomnia. It might appeal to horror fans as Karloff has an early (but small) role in it, but that's about it.

I wouldn't be surprised if it was an "extra" either, but if Fox does go that route, I hope it is on the last box set as anyone unfamiliar with Chan would get the wrong impression from watching it and perhaps not seek out the films from the series proper.