Change of behavior: 3.80 vs 3.81beta3 WRT line continuation

[Steve James]

AFAICT the behavior of line continuation escapes has changed within 
single-quoted strings. What's really confusing me is that this seems to be 
deliberate.

Here's the simple example make script

all:
        @echo 'line1\
line2'


Version 3.80 prints this (as I would expect):
line1line2

But Version 3.80beta3 prints this:
line1\
line2


There's some background to this change concerning POSIX (Savannah bug # 1332). 
Revision 1.166 of job.c is concerned. Here's the relevant code section:

          /* Inside a string, just copy any char except a closing quote
             or a backslash-newline combination.  */
          if (*p == instring)
            {
              instring = 0;
              if (ap == new_argv[0] || *(ap-1) == '\0')
                last_argument_was_empty = 1;
            }
          else if (*p == '\\' && p[1] == '\n')
            {
              /* Backslash-newline is handled differently depending on what
                 kind of string we're in: inside single-quoted strings you
                 keep them; in double-quoted strings they disappear.  */
              if (instring == '"')
                ++p;
              else
                {
                  *(ap++) = *(p++);
                  *(ap++) = *p;
                }
              /* If there's a TAB here, skip it.  */
              if (p[1] == '\t')
                ++p;
            }

See, entirely deliberate. What's more the regression tests in 
tests/scripts/misc/general3 verify this behavior. But this all looks broken 
to me.

So what's up? Is this
1. A new bug in the beta,
2. A deliberate non-backward compatibility
3. Something else that's confusing me?

Thanks,
Steve.

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