If anyone has come across this before I'd love to know!
I'm using the CartesianDataCanvas in Flex to add background
images behind my chart line.
Visually this is working fine. In order for the line to stay
in front of the image, I've set the alpha on the background image
to 0.3 and the line's aplha to 1. The problem is that some of the
data tips for the line chart to not show up when I hover over the
part of the line that is in front of the image.
They work fine in the other parts of the chart.
I'm using this method to add the image.