Slicer Months shows <, > values as well.

I'm sure I've seen this solved somewhere, but I can't find it now....I have a list of dates in a table, and a pivot from that table, with a Slicer (by month) to let me select the data by month. The slicer shows the months OK, but also includes (for instance) Jan 2014, >1/1/14, Feb 2015, <28/2/14.
Where do the "less than / Greater than" entries come from, and how do I get rid of them ?

Thanks oh wise ones...

OldMan62