[Voted into WP at October, 2009 meeting.]

Proposed resolution (July, 2009):

Change 7.6.2.5 [expr.sizeof] paragraph 1 as follows:

...The sizeof operator shall not be applied to an expression that has function or incomplete type, or to an enumeration type whose underlying type is not fixed before all its enumerators have been declared, or to the parenthesized name of such types, or to an lvalue that designates a bit-field...

There is no reason for the prohibition of using sizeof on “an enumeration type before all its enumerators have been declared” (7.6.2.5 [expr.sizeof] paragraph 1) if the underlying type of the enumeration is fixed.