when color.alternate is set to change the background, bold is always removed from text on alternate rows

Running taskwarrior 2.6.1.

When color.alternate is set to change the background with "on _something_", bold is removed from the rows that have the alternate background.

For example: `color.alternate=on gray5`

Even if I set bold on color.alternate (example: `color.alternate=bold magenta on gray5`) it will not be bold on the row with the gray5 background. In the give example text color will change to magenta (when no other higher priority color applies), but it won't turn bold. Lines that would normally be bold, will have bold removed on the lines with gray5 background.

If I don't set "on _something_" in color.alternate (for example: `color.alternate=magenta`), then bold will be preserved.

If I set bold for alternate (eg. `color.alternate=bold magenta`), alternate rows will be bold (and magenta).

To sum up: if background is not set in color.alternate it will work as expected, but if "on _somecolor_" is set, bold is always removed from alternate rows.