Problem with composition mode with multiple displays

Scrivener 2.5; OSX 10.9; MacBook Pro mid-2010.
Extra display plugged via mini Display port to DVI.

Whenever I use Scrivener on one screen (normal view or full screen), if I press on the composition mode button, the composition view always swaps screen.

Origin: MBP screen -> composition mode appears on external display
Origin: external display -> composition mode appears on MBP screen

Could not find report of this behavior on the website.

Any idea what is causing this?

Thanks
Mathieu

There is actually a preference that will make it work like that, as some do prefer it that way. Check and make sure that “Use secondary screen if available” is unchecked, in the Compose preference pane, upper-left corner.