Non-compliance of \c for echo and print builtins

[Daode]

Hello!
This

  echo dash:
  dash -c 'echo "\ttab\tul\cau\tau"'

  echo; echo bash:
  bash -c 'echo -e "\ttab\tul\cau\tau"'

  echo; echo ksh:
  ksh -c 'echo -e "\ttab\tul\cau\tau"'

  echo; echo mksh, echo:
  mksh -c 'echo -e "\ttab\tul\cau\tau"'
  echo; echo mksh, print:
  mksh -c 'print "\ttab\tul\cau\tau"'
  echo

prints

  dash:
    tab ul
  bash:
    tab ul
  ksh:
    tab ul
  mksh, echo:
    tab ulau    au
  mksh, print:
    tab ulau    au

POSIX says:

  \c
    Suppress the <newline> that otherwise follows the final
    argument in the output. All characters following the '\c' in
    the arguments shall be ignored.

Verified it's still true for "R46 2013/06/03".
I couldn't brace myself up for patching the test script.
Ciao,

--steffen