diff --git a/ui/dr-ui/ui/masks.slint b/ui/dr-ui/ui/masks.slint
index 1851779..aacccea 100644
--- a/ui/dr-ui/ui/masks.slint
+++ b/ui/dr-ui/ui/masks.slint
@@ -137,10 +137,18 @@ component MaskEntry inherits Rectangle {
                 alignment: center;
                 spacing: 0px;
 
+                // Both lines below are bounded for the reason the subject
+                // row is: a mask's label and kind come from the model, and an
+                // unbounded `Text` asks for its whole string at layout time
+                // even when `elide` means it will never draw it. A mask *is* a
+                // segmentation result, so without this the column moved when a
+                // subject was clicked as well as when one was found.
                 Label {
                     text: root.data.label;
                     emphasised: root.data.selected || touch.has-hover;
                     overflow: elide;
+                    min-width: 0px;
+                    max-width: 160px;
                 }
 
                 Caption {
@@ -148,6 +156,8 @@ component MaskEntry inherits Rectangle {
                     // targets in a row, and wrapping would give the rows of a
                     // stack different heights for no gain.
                     overflow: elide;
+                    min-width: 0px;
+                    max-width: 160px;
                     // Three states worth distinguishing, and each has a
                     // different remedy: stale needs the segmentation re-run,
                     // unadjusted needs a slider moved, and the ordinary case
@@ -418,6 +428,30 @@ export component MaskPanel inherits Rectangle {
                         emphasised: subject-row.has-hover;
                         horizontal-stretch: 1;
                         overflow: elide;
+                        // **`elide` is a paint-time behaviour, and this is a
+                        // layout-time problem.** A `Text` asks for the width of
+                        // its whole string whether or not it will draw all of
+                        // it, so without a stated maximum this row asked for
+                        // whatever the model happened to return, that became
+                        // `layout.preferred-width`, the panel publishes that as
+                        // its `min-width`, and the develop column takes the
+                        // widest minimum any panel declares. The column
+                        // therefore moved the instant segmentation finished —
+                        // a photograph the user was looking at, jumping
+                        // sideways because a label said "traffic light".
+                        //
+                        // Stated as a maximum for the reason `ChipGrid`
+                        // declares its width from its column count rather than
+                        // from its options: what a panel asks for must follow
+                        // from its structure, never from its data. Past this
+                        // the row elides, which is what `elide` was for.
+                        //
+                        // 160px is the same judgement as `ChipGrid`'s 88px
+                        // chip — comfortable for the class names this model
+                        // returns, and narrow enough that a subject list
+                        // cannot be what sets the column.
+                        min-width: 0px;
+                        max-width: 160px;
                     }
                     Value { text: round(subject.score * 100) + "%"; }
                 }