I do not know the answer to this, but can you post a packaged workbook that demonstrates this issue so I can test on my end to see if I get the same result?
Hi William and Matt, I too have similar issue and after trying a while, I am using the 201304 format.
If William doesn't get answered, I will post my Scenario.
I hope I understand correctly your scenario and requirement.
To reach your requirement I created a Calculated Field called Year-Month selector using the formula:
DATENAME('year',[Order Date])+" - "+DATENAME('month',[Order Date])
Then I added this new field in Filter, show the Quick Filter and define a Single Value (Slider)
It is working Ok for me. See the attached workbook.
I hope this helps
Year_Month_Slider_RM.twbx 1.2 MB