Go to Presentation tab and uncheck Pop up label and change the text as pop up expression as below
= 'Dimension =' & Dimension& chr(10)& 'Multiplied = ' & sum([Metric 1])*sum([Metric 2])
1 - Disabling 'pop-up labels' in presentation tab of your chart properties, in the middle of the bottom section on Presentation Tab
2 - Change the third expression in the Expression Tab to this
='Metric Value = ' & Dimension & Chr(10)
'Multiplied = '
& sum([Metric 1])*sum([Metric 2])
You can Change the 'Metric Value' for the third expression to anything you want, like Dimension Value or whatever
Some more searching on this led me to find that this is a confirmed bug since 11.20 SR7 which is solved in 11.20 SR10.
The release notes of SR10 contain this line under "Bugs solved in SR10":
69025 [Text as Pop-up] in [Chart Properties] -> [Expressions] doesn't pop up custom message since QV11.2 SR7
See this on page 24 of this release notes document:
So I guess we'll have to upgrade to get this functionality back.
Thanks for the help.