This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 110b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
[Voted into the WP at the March, 2011 meeting as part of paper N3262.]
A user-defined literal like 0x123DZ could be parsed either as a hexadecimal-literal of 0x123 and a ud-suffix of DZ or as a hexadecimal-literal of 0x123D and a ud-suffix of Z. There does not appear to be a rule that disambiguates the two possible parses.
Proposed resolution (November, 2010) [SUPERSEDED]:
Change 5.13.8 [lex.ext] paragraph 1 as follows:
If a token matches both user-defined-literal and another literal kind, it is treated as the latter. [Example: 123_km, 1.2LL, "Hello"s are all user-defined-literals, but 12LL is an integer-literal. —end example]