The message "SHOULD NOT BE SEEN" is displayed when using a user defined macro:

Create a macro to invert an object (not a point) with respect to a circle.
Then invoke the macro and hover on an "invertible" object (a circle, an arc, a line, a ray or a segment).

A minimal patch could be:

--- a/objects/special_imptypes.cc
+++ b/objects/special_imptypes.cc
@@ -111,7 +111,7 @@ WeightImpType weightimptypeinstance(
 
 InvertibleImpType::InvertibleImpType( const ObjectImpType* parent,
     const char* internalname )
-  : ObjectImpType( parent, internalname, snbs, snbs,
+  : ObjectImpType( parent, internalname, snbs, I18N_NOOP( "Select this object" ),
                    snbs, snbs, snbs, snbs, snbs, snbs, snbs )
 {
 -----------------------------------------------------------------------------------

Since the message "Select this object" is already present somewhere else, this should not
require any additional work by the localization teams.