I just made ADRs this morning and that came up on one of my confirmations.
I've never given it any thought - they won't split up parties, unless it was a really huge number of people. Even then, they do try to accommodate - last summer we went to Breakfast at O'hana's and one of the tour groups was there, and there was numerous tables pushed together in the middle of the room as there was about 30 kids and chaperones sitting there.
Even then we were seated and all was fine as we are a party of 4.
I think sometimes it's just the "computer" acting like a "computer".
If you have any concerns, just mention it when you check in at the podium.