diff --git a/docs/ISSUES.md b/docs/ISSUES.md
index b5cb17fc..092df1c4 100644
--- a/docs/ISSUES.md
+++ b/docs/ISSUES.md
@@ -3765,6 +3765,43 @@ Scan data: standing-now → [0x103]; flip-a → []; flip-b → [0x100].
 
 ---
 
+## #113 — Phantom exterior staircase on an A9B3 building (not in retail); suspect misplaced interior cell
+
+**Status:** OPEN
+**Severity:** MEDIUM (visual fidelity; suspect shares a root with the same
+building's containment gap #112 and collision gaps #99)
+**Filed:** 2026-06-10 (late — user side-by-side vs retail)
+**Component:** render / building cells (or dat interpretation)
+
+**Symptom:** an A9B3 building (near the #112 hill cottage; NPCs Aun Kielerea +
+The Sentry nearby, spot ~(183, −111, 116) world) shows a stone-and-wood
+STAIRCASE attached to its exterior wall in acdream; the retail client shows a
+plain wall with a window there (user screenshots, 2026-06-10). The stairs are
+NOT pickable (clicks select only NPCs behind them) ⇒ not a stab/WorldEntity —
+building-shell or interior-cell geometry.
+
+**Hypothesis (would unify three symptoms at this building):** a misplaced
+interior EnvCell — an indoor staircase cell whose world transform puts its
+geometry outside the shell. That would simultaneously explain (a) the phantom
+exterior stairs, (b) the interior containment gap (#112's dead zone = a cell
+volume sitting in the wrong place), and (c) missing collision on objects in
+the house.
+
+**Next steps:** (1) ACViewer oracle — open the same landblock; stairs present
+there ⇒ shared dat-interpretation, absent ⇒ our transform/draw
+(feedback_acviewer_as_oracle). (2) Offline: dump A9B3's LandBlockInfo
+buildings + per-cell Position.Origin/rotation; look for a cell whose
+transformed AABB escapes the building footprint. (3) Identify the building id
+(the landblock's building list near the spot).
+
+**Meta (user, 2026-06-10):** "we should not have to verify all houses like
+this" — agreed; the open systemic debts are A6.P4 per-cell shadows (#99,
+fixes collision everywhere), the #112 residual oracle read, and this transform
+check. If (2) finds a systematic per-building transform error, ONE fix covers
+every affected house.
+
+---
+
 # Recently closed
 
 ## #111 — ACE-mutated indoor restores: transparent interior / wrong placement at login — [DONE 2026-06-10 · 5f1eb7c + 5706e0e + 2735695]