What you were expecting to happen, and what actually happened?
I was just browsing through my troops, thinking about mechanics that I could use to annoy attackers. I was expecting to find all Troops/Weapons that can inflict Death Mark when I put “death mark” in the search box…
In vain! 
Do you have any screenshots or video you want to share with us so we can see the problem? Attach them to your post!
To clarify (since it confused me), the OP seems to be saying:
“The game inconsistently uses ‘Death Mark’ (with a space) and ‘Deathmark’ (with no space) in the text, which makes it hard to search for this effect via the troop list search field.”
I swear I mentioned this when 1.0.9 hit… Sirrian? Embrace consistency! “Death Mark” or “Deathmark”, one not both.
Make Mab easier to understand while you’re at it please.
OH MY GOD SPOILERS
