Do not restrict width of hidden text area (can cause bumping of the screen as the screen scrolls to follow the cursor as it wraps to a new line in the zero-width area). Hide off bottom right (instead of upper left).

guacamole/src/main/webapp/styles/client.css

@@ -217,11 +217,9 @@ div#viewportClone {
 textarea#eventTarget {
     position: fixed;
    
-    /* Zero... zero... zero... zero... zero... */
+    /* Hide offscreen */
-    right: 0;
+    left: 100%;
-    bottom: 0;
+    top: 100%;
-    width: 0;
-    height: 0;
     opacity: 0;
 
     overflow: hidden;