The Wood Elf Glade Guard with Starfire Shafts are taking attrition due to lack of vampire corruption and if you hover over the units attrition symbol is uses the line "undead creatures cannot survive without the taint...etc etc" (what ever the usual undead attrition text is).
1.Start up game
2.Select Wood Elves Grand Campaign (or Argwylon)
3. Start Grand Campaign
4. Obtain the ability to recruit Glade Guard with Startfire Shafts (or wait for a wood elf rebellion to spawn with this unit in)
5. Recruit GG with SS
6. Observe that when moving around on the Campaign Map that they are receiving undead attrition.
Note: I have not yet recruited them for myself but will update the bug with evidence when I do. I will also update if for some reason it only effects the AI's version of this unit.
This is 100% repro so far. Every enemy/ally wood elf army with this unit takes attrition (that unit no the entire army).