Fix Surface Deform not unbinding if target is removed

release/scripts/startup/bl_ui/properties_data_modifier.py

@@ -969,11 +969,11 @@ class DATA_PT_modifiers(ModifierButtonsPanel, Panel):
         layout.separator()
 
         col = layout.column()
-        col.active = md.target is not None
 
         if md.is_bound:
             col.operator("object.surfacedeform_bind", text="Unbind")
         else:
+            col.active = md.target is not None
             col.operator("object.surfacedeform_bind", text="Bind")
 
     def UV_PROJECT(self, layout, ob, md):

source/blender/modifiers/intern/MOD_surfacedeform.c

@@ -1195,7 +1195,7 @@ static bool isDisabled(ModifierData *md, int UNUSED(useRenderParams))
 {
 	SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;
 
-	return !smd->target;
+	return !smd->target && !(smd->verts && !(smd->flags & MOD_SDEF_BIND));
 }
 
 ModifierTypeInfo modifierType_SurfaceDeform = {