Dates against numbers in Calc

I have a LibreOffice Calc sheet with two columns of data.
Column A is headed Date, and contains dates.
Column B is headed ID and contains numbers.

If I produce a line graph with this data,
the dates appear along the abscissa (x-axis),
the IDs appear along the ordinate (y-axis) and
there is a black graph line of IDs against dates.

If I switch the columns so that
Column A is headed ID and contains numbers,
Column B is headed Date, and contains dates and
I produce a line graph with this data,
sequential numbers appear along the abscissa (x-axis),
the IDs appear along the ordinate (y-axis) and
there are two coloured graph lines in the graph:
a blue graph line labelled ID, and
a red graph line labelled Date.

How can I produce a graph of dates against IDs?

LibreOffice version: 25.2.0.3 (X86_64) / LibreOffice Community
Build: e1cf4a87eb02d755bce1a01209907ea5ddc8f069

ask117697.ods (25.9 KB)