diff --git a/frontend/src/stores/__tests__/canvasStore/sizing.test.ts b/frontend/src/stores/__tests__/canvasStore/sizing.test.ts
index 7c21529..cf3b996 100644
--- a/frontend/src/stores/__tests__/canvasStore/sizing.test.ts
+++ b/frontend/src/stores/__tests__/canvasStore/sizing.test.ts
@@ -118,4 +118,53 @@ describe('canvasStore — sizing & z-order', () => {
     useCanvasStore.getState().updateNode('r1', { properties: [] })
     expect(useCanvasStore.getState().nodes.find((n) => n.id === 'r1')?.height).toBe(240)
   })
+
+  // Regression (#278): editing any field on a container-mode vm/lxc/docker_host host used to
+  // reset its manually-set height to undefined, snapping it back to auto-fit size and
+  // scrambling nested children. Only proxmox was excluded. Keep the manual height for every
+  // container-mode host type.
+  it.each(['vm', 'lxc', 'docker_host'] as const)(
+    'updateNode preserves manual height for a container-mode %s when properties change',
+    (type) => {
+      const host: Node<NodeData> = {
+        id: 'h1',
+        type,
+        position: { x: 0, y: 0 },
+        width: 400,
+        height: 300,
+        data: { label: type, type, status: 'unknown', services: [], container_mode: true },
+      }
+      useCanvasStore.setState({ nodes: [host], edges: [] })
+      useCanvasStore.getState().updateNode('h1', { properties: [], label: 'renamed' })
+      expect(useCanvasStore.getState().nodes.find((n) => n.id === 'h1')?.height).toBe(300)
+    }
+  )
+
+  it('updateNode still resets height for a vm NOT in container mode when properties change', () => {
+    const leaf: Node<NodeData> = {
+      id: 'v1',
+      type: 'vm',
+      position: { x: 0, y: 0 },
+      width: 200,
+      height: 120,
+      data: { label: 'vm', type: 'vm', status: 'unknown', services: [], container_mode: false },
+    }
+    useCanvasStore.setState({ nodes: [leaf], edges: [] })
+    useCanvasStore.getState().updateNode('v1', { properties: [] })
+    expect(useCanvasStore.getState().nodes.find((n) => n.id === 'v1')?.height).toBeUndefined()
+  })
+
+  it('updateNode preserves height for a proxmox host when properties change', () => {
+    const px: Node<NodeData> = {
+      id: 'px1',
+      type: 'proxmox',
+      position: { x: 0, y: 0 },
+      width: 500,
+      height: 350,
+      data: { label: 'px', type: 'proxmox', status: 'unknown', services: [], container_mode: true },
+    }
+    useCanvasStore.setState({ nodes: [px], edges: [] })
+    useCanvasStore.getState().updateNode('px1', { properties: [] })
+    expect(useCanvasStore.getState().nodes.find((n) => n.id === 'px1')?.height).toBe(350)
+  })
 })
diff --git a/frontend/src/stores/canvasStore.ts b/frontend/src/stores/canvasStore.ts
index c3ef3d3..2ad4202 100644
--- a/frontend/src/stores/canvasStore.ts
+++ b/frontend/src/stores/canvasStore.ts
@@ -13,6 +13,7 @@ import { generateUUID } from '@/utils/uuid'
 import { normalizeHandle, removedHandleIds, handleCountField, sideDefault, handleId, SIDES } from '@/utils/handleUtils'
 import { applyOpacity } from '@/utils/colorUtils'
 import { readHideIp, writeHideIp } from '@/utils/ipDisplay'
+import { CONTAINER_MODE_TYPES } from '@/utils/virtualEdgeParent'
 
 type HistoryEntry = { nodes: Node<NodeData>[]; edges: Edge<EdgeData>[] }
 type Clipboard = { nodes: Node<NodeData>[]; edges: Edge<EdgeData>[] }
@@ -325,8 +326,13 @@ export const useCanvasStore = create<CanvasState>((set) => ({
       let nodes = state.nodes.map((n) => {
         if (n.id !== id) return n
         const updated: Node<NodeData> = { ...n, data: { ...n.data, ...data } }
-        // When properties change, clear stored height so the node auto-sizes to fit new content
-        if ('properties' in data && n.data.type !== 'proxmox' && n.data.type !== 'groupRect' && n.data.type !== 'group') {
+        // When properties change, clear stored height so the node auto-sizes to fit new content.
+        // A container-mode host (vm/lxc/docker_host) keeps a manually-set height: resetting it
+        // snaps the container back to auto-fit size and scrambles its nested children (#278).
+        // proxmox is always excluded (legacy behavior); the other container types are excluded
+        // only while actually in container mode.
+        const isContainerHost = CONTAINER_MODE_TYPES.has(n.data.type) && !!n.data.container_mode
+        if ('properties' in data && n.data.type !== 'proxmox' && n.data.type !== 'groupRect' && n.data.type !== 'group' && !isContainerHost) {
           updated.height = undefined
         }
         if ('parent_id' in data) {
diff --git a/frontend/src/utils/virtualEdgeParent.ts b/frontend/src/utils/virtualEdgeParent.ts
index 9cef306..838fef1 100644
--- a/frontend/src/utils/virtualEdgeParent.ts
+++ b/frontend/src/utils/virtualEdgeParent.ts
@@ -2,7 +2,7 @@ import type { NodeData } from '@/types'
 
 export type NodeType = NodeData['type']
 
-const CONTAINER_MODE_TYPES = new Set<NodeType>(['proxmox', 'vm', 'lxc', 'docker_host'])
+export const CONTAINER_MODE_TYPES = new Set<NodeType>(['proxmox', 'vm', 'lxc', 'docker_host'])
 const DOCKER_CONTAINER_PARENT_TYPES = new Set<NodeType>(['docker_host', 'lxc', 'vm', 'proxmox'])
 
 export interface VirtualEdgeEndpoint {