Text box information in Chart disappears when published to SharePoint

[PauseToThink]

I'm using a text box with a formula in my chart to show the current high value on the entire chart. It works fine in Excel (2013) but when I publish to SharePoint (2013) the data disappears. A text box with static data shows fine in SharePoint. My formula is a simple cell reference (='Table Name'!$A$1) that I type in the formula bar.
I've tried bringing the text box to the front. Mmaking the chart area transparent (in case it's covered up). No joy.