1) any items that are completely off the artboard won't actually be rendered (might not be in the svg/fxg, didn't check). Simple solution: group it all together.
2) the "height" value of your object in flash will no longer be correct. it'll report half its height (and half its width) because the height and width of the asset "outside" of the artboard (or "viewport" in the svg/fxg) isn't counted. So be sure to compensate.
The other option being to register your object top left at 0,0... but that gets annoying in code, imo.
Would love to hear other suggestions, now that I finally had this breakthrough. ;)