The fix will be out in the upcoming Tiled 1.1.4 and the next development snapshot. I plan to release a new snapshot in the next two days. Not sure yet when it’s time for 1.1.4 since there’s some other issues to be looked into as well.
As a workaround, you can Save instead of Export your tileset in JSON format. Just beware that this will probably change the tileset reference in maps saved afterwards.