Can't set default type to "Clustered Column"

[MikeA.]

Hello.

I can create a default chart type for ANY of the types/sub-types EXCEPT
for Column/Clustered Column.

When I select an existing chart and change it to Column/Clustered
Column, and then set it as the default, the existing chart will change
to the new style, but for any successive charts, Excel reverts back to
the Column/Stacked Column style.

For any other type (Bar, Pie, etc., etc.), existing and successive
charts will appear as I've set them. I just can't get Excel to keep my
default selection of Column/Clustered Column.

Anyone have any ideas why this might be happening, and what I might be
able to do to fix it?

Many thanks.