After toying with that order for some time I noticed the following things:
- 1 Xyphos Wing is regarded as sufficient for "patrol", but mightier ships like the Tempest or Hyperion need additional craft
It might be considering an individual Xyphos fighter in the same category as a Tempest or Hyperion, since both of those are "small" frigates and the Xyphos is a fairly hefty fighter in its own right
This seems to be the case, if one Xyphos is destroyed the remaining one is treated like any other frigate/heavy wing and get's assistance. Still a bug though, a single Xyphos is inferior to frigates and heavy wings. To upgrade the AIs judgement for elite frigates could also be a solution, if the stood together with the Xyphos wing on the "only one unit needed" pedestal it would not seem strange.
I noticed another issue: Sometimes up to five units react to a patrol order. I had a Talon wing, a Longbow wing, a Hound and a Shade fly to a single navpoint, that are 21FP. Another time 3 Talon Wings and 2 Hounds (15FP).
I have no clue how the assignment and prioritization for "patrol" is supposed to work, but this seems to much.