I have a similar situation as @iamjasona
I made a segment. First I create a date (custom date example begin in August 23, 2017 until September 2017) as a condition with another dimension. I include both on a container to not interfere with my others containers that I create with dimensions only.
The segment was working correctly a few weeks ago, I saw now that all my data begin with the date (August 23, 2017) instead of one container only?
Did something change in the relationship between the containers?