Because Adobe Systems bought the swf technology when they acquired Macromedia (who bought the technology from a small start-up company), they have their "rules" as to what animation types for certain objects can and cannot be done.

And Xara's animation engine is based around SWF standards, regardless of whether you export to GIF, swf, or AVI. When you "break a rule", such as changing a gradient from frame to frame, Xara lets you know (sort of) that it's ceased to be a supported tweening object and it will be written as a key frame that doesn't tween with the following frame but rather just sits there for its allotted duration and hence some animations are large, and look a little choppy.

If you want to do tweening Xara-style (and Adobe style), I wrote a long list of what you can and cannot expect from a Xara animation

here a while back. Scroll down to the "Read Me First" section—the text is live so you can copy it to a local document and refer to it in the future.

My Best,

Gary