My organization has recently noticed an issue when applying advanced segments to visit counts during different time ranges.

With no advanced segments turned on, here are the visit counts for Oct 1st - Oct 4th during the time range Sept 8th - Oct 8th:

Oct 1 - 7
Oct 2 - 7
Oct 3 - 8
Oct 4 - 5

Again, with no advanced segments turned on, here are the visit counts for Oct 1st - Oct 4th but I've changed the time range to Oct 1st - Oct 4th. As expected, the numbers are the exact same as above:

Oct 1 - 7
Oct 2 - 7
Oct 3 - 8
Oct 4 - 5

Now, I turn on the "Non paid search traffic" advanced segment. Here are the visit counts for Oct 1st - Oct 4th during the time range Sept 8th - Oct 8th:

Oct 1 - 0
Oct 2 - 0
Oct 3 - 0
Oct 4 - 2

Here is where it gets weird. I keep the advanced segment on, and change the time range to Oct 1st - Oct 4th. This is what I get for the exact same dates as above:

Oct 1 - 4
Oct 2 - 2
Oct 3 - 6
Oct 4 - 5

We've found the same inconsistency in our other GA profiles that get much more traffic (the above numbers come from one of our specialized topic blogs), but the inconsistency is less pronounced where there are more visits. My question is: why are the visit counts different for different time ranges when advanced segments are turned on, but exactly the same when no advanced segments are applied? Is this a GA bug or am I missing something about how the advanced segments work?