Not sure if this came up before... When you enter turn-based mode to prebuff your party before combat (blade ward, haste, ...) and only a subset of the party enters the combat (because of hiding, positioning, whatever) then those party members who didn't enter combat will automatically exit turn-based mode and their prebuffs start to expire.
I usually forget about this. It caused quite a few reloads.
Why not keep everyone in turn-based mode independent of whether they entered combat or not?