Suggested resolution:

Change in 5.5 [lex.pptoken] bullet 5.4.1 as follows:

• ...
• Otherwise, the next preprocessing token is the longest sequence of characters that could constitute a preprocessing token, even if that would cause further lexical analysis to fail, except that
  • a string-literal or user-defined-string-literal token is never formed when a header-name token can be formed, and
  • a header-name (5.6 [lex.header]) is only formed ...

Consider:

  #define SUFFIX
  #include "foo.h"SUFFIX

The "foo.h" should be lexed as a header-name, not as a user-defined-string-literal.