Elven Ranger attacks goodly character?

[Tami]

You hear the sound of footsteps from the north-west.
A stirge flies in from the north-west.
A stirge approaches you and prepares to engage you in combat!
A stirge evades your crushing attack.
Someone joins the battle!
A stirge causes you to vibrate with pain, the sound of ethereal laughter echoing in your ears.
An elven ranger fades into visibility.
Suddenly an elven ranger attacks you off guard!
You duck under an elven ranger's slashing attack.
You duck under an elven ranger's slashing attack.
An elven ranger's slash minces your left leg.
Your crush beats a stirge to a bloody pulp.
A stirge is stunned, but will probably recover.
An elven ranger's slash lacerates your abdomen.
You hear the howl of a wild animal nearby.
You score a critical hit!
Your crush beats a stirge to a bloody pulp.
A stirge is DEAD!
Suddenly an elven ranger attacks you off guard!
Suddenly an elven ranger attacks you off guard!
You wish that your wounds would stop BLEEDING so much!
With a sickening sound an elven ranger's slash violently shreds your abdomen.
You wish that your wounds would stop BLEEDING so much!
An elven ranger evades your crushing attack.
An elven ranger's slash nearly bisects your left leg.
Your pulse returns to normal.

[Harroghty]

As noted on the Ask Channel, this is not a bug per se. The game compares the alignments of the combatants and makes decisions about who should join who. Regardless of your PC's alignment being good, the ranger and the stirge had a closer alignment match and thus he attacked your PC. If you want to put an IC spin on it, then this ranger likes the wildlife more than a human interloper in his forest.