Possible bug with chart y axis custom number formatting

Hi,

I think there might be a bug with the way custom number formatting is applied to chart y axes. I have some simple data ranging from -5000000 to 5000000 and I have applied the following number format to that column:

#,##0,,.0;(#,##0,,.0);-

When I put that data in a chart and set the y axis display units to 'none' (instead of auto) then I get the following chart - note the correct number formatting on the positive part of the axis but the incorrect format on the negative side:

The table below the chart shows the same data with the same number formatting just in a table (to illustrate that it works just fine there).

If I change the number format to the following then everything works ok, so it looks like it's something to do with the parenthesis in the number format:

#,##0,,.0;-#,##0,,.0;-

Is this expected behaviour? If so, what do I need to do to get my negative number format to work correctly in the chart (I need to use brackets for the negative values)? I don't want to use the display units setting as we don't want the 'M' next to the millions.

Thanks,

Ben