transition.to alpha=0

Solar2D Android
#1 
transiton.to( img, {time=600, alpha=0, onComplete=function(event)  
 img.isVisible = false  
 loadSomeOtherStuff()  
end)

There is a noticeable delay near the end where the img is partially visible, but mostly transparent in this code. Any ideas why that might occur? [import]uid: 4596 topic_id: 10078 reply_id: 310078[/import]