The problem arises when manually setting the X-axis "from" and "to" properties (right click, properties, x-axis).
For some reason, the issue is when setting the date to 00:00:00 on the 1st day of any Year-Month (YYYY/MM/01 00:00:00). The date is saved in the .plc as 24:00:00 on the last day of the previous month - which the Plot Composer fails to read correctly. The fix is currently to add 1 second to the DateTime (or not to use the Day 1 @ 00:00:00).
It appears that the Background data have [i]already[/i] been imported.
When the data is still in the background (not imported) the Water points will be green and the land-boundary will be red. [img width=200 height=104]http://i.imgur.com/iZAHebg.png[/img]
When you click on the "Import from Background" button and select the data, they will highlight as red. [img width=200 height=103]http://i.imgur.com/iO6m0Sx.png[/img]
Clicking again on the "Import from Background button finally imports the data. The imported data will now appear as blue dots (water) and a dark green boundary (land-boundary). [img width=200 height=103]http://i.imgur.com/K5eFu7c.png[/img]