The 'duplicate layer' function in the GAP's Frames Modify dialog permits you to
create a layer that does not have an alpha channel. This doesn't really create
any problems, but I recall seeing in Bugzilla that this should not be possible
(this was just a side comment to another issue and I was unable to locate the
report). Also, I am unaware of any other way to create such an non-background
alpha-less layer and wonder if this behavior should be changed to match the
GIMP's Duplicate Layer functionality.
Gimp-user mailing list