[Moved to DR at the April, 2013 meeting.]

Proposed resolution (October, 2012):

Change 7.7 [expr.const] paragraph 2 as follows:

• ...

• a typeid expression (7.6.1.8 [expr.typeid]) whose operand is a glvalue of a polymorphic class type;

One of the criteria in 7.7 [expr.const] paragraph 2 for disqualifying an expression from being a constant expression is:

• a typeid expression (7.6.1.8 [expr.typeid]) whose operand is of a polymorphic class type;

on the basis that a runtime test for the dynamic type is inconsistent with a constant expression. However, it is only glvalues of polymorphic type that require a runtime test; type-ids and prvalues with a polymorphic type could (and should) be permitted in constant expressions.