To duplicate this bug, create a chart with two lines with an x-axis
that contains consecutive dates. Then, add a plot chart series (again
with date x-axis) and add data labels to it. IMPORTANT: Then, change
the plot chart to plot using the primary axis. Finally, save and
reopen the file. The data labels disappear and you cannot re-add them.

I think I have it.
"Plot chart" = XY chart
Also we need to format the Line chart to have the x-axis labels aligned with
tick marks before adding the third series
But I find that the data labels are still visible after changing third
series to Primary Axis.
Also: why would we want to mix Line and XY when the dates are consecutive?
--
Bernard V Liengme
Microsoft Excel MVP
http://people.stfx.ca/bliengme
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"Blake M" <(E-Mail Removed)> wrote in message
news:3fc8beb4-f245-4cb6-9907-(E-Mail Removed)...
> To duplicate this bug, create a chart with two lines with an x-axis
> that contains consecutive dates. Then, add a plot chart series (again
> with date x-axis) and add data labels to it. IMPORTANT: Then, change
> the plot chart to plot using the primary axis. Finally, save and
> reopen the file. The data labels disappear and you cannot re-add them.