2 checks in FeatureInfoPanel.js:
1) no layers with GFI available:
this.olControl.layers are visible layers with GFI enabled
// No layers with GFI and no features from Vector layers available: display message
if (this.olControl.layers.length == 0 && this.features == null) {
this.handleNoGetFeatureInfo();
}
2) no features found: display text
I now realize that the first check does not take visible Vector layers into
account....