diff --git a/client/src/components/vbox.component.jsx b/client/src/components/vbox.component.jsx
index bb9751eb..97a7c049 100644
--- a/client/src/components/vbox.component.jsx
+++ b/client/src/components/vbox.component.jsx
@@ -177,7 +177,7 @@ class Vbox extends preact.Component {
         }
 
         function availableBtn(v, group, index) {
-            if (!v) return <button disabled class='empty' key={(group + 1) * index} >&nbsp;</button>;
+            if (!v) return <button disabled class='empty' key={(group * 10 + index} >&nbsp;</button>;
             const selected = vboxSelected[0] === group && vboxSelected[1] === index;
 
             // state not yet set in double click handler