Proposed resolution (February, 2012):

Change 15.7 [cpp.replace] paragraph 12 as follows:

If there is a ... in the identifier-list immediately preceding the ) in the function-like macro definition, then the trailing arguments, including any separating comma preprocessing tokens, are merged to form a single item: the variable arguments variable arguments. The number of arguments so combined is such that, following merger, the number of arguments is one more than the number of parameters in the macro definition (excluding the ...).