I think it depends on at what exact point the shell is doing the 2>&1 redirection.

I can't reproduce the problem with the command you've shown, i.e. here I do get

$ ./826946.pl
CMD        : >>echddo 'arghh'<<
RETURN_CODE: >>32512<<
CMD_RESULT : >>sh: echddo: not found
<<
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but when I remove one single quote ($cmd = "echddo arghh'"), so the shell command has a syntax error, I get like you

$ ./826946.pl
sh: Syntax error: Unterminated quoted string
CMD        : >>echddo arghh'<<
RETURN_CODE: >>512<<
CMD_RESULT : >><<
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The corresponding straces reveal that the redirection simply isn't being done in the latter case (note the missing dup2(1,2) ), presumably because my shell does the syntax checking before the 2>&1 redirection (which makes sense...), while in the other case, it does the redirection before starting to look for an executable 'echddo':

( cmd:  echddo 'arghh' 2>&1 )
...
[pid 15950] rt_sigaction(SIGTERM, NULL, {SIG_DFL}, 8) = 0
[pid 15950] rt_sigaction(SIGTERM, {SIG_DFL}, NULL, 8) = 0
[pid 15950] fcntl(2, F_DUPFD, 10)       = 10
[pid 15950] close(2)                    = 0
[pid 15950] fcntl(10, F_SETFD, FD_CLOEXEC) = 0
[pid 15950] dup2(1, 2)                  = 2
[pid 15950] stat("/home/almut/bin/echddo", 0x7fffb62454b0) = -1 ENOENT
+ (No such file or directory)
[pid 15950] stat("/usr/local/sbin/echddo", 0x7fffb62454b0) = -1 ENOENT
+ (No such file or directory)
[pid 15950] stat("/usr/local/bin/echddo", 0x7fffb62454b0) = -1 ENOENT 
+(No such file or directory)
[pid 15950] stat("/usr/sbin/echddo", 0x7fffb62454b0) = -1 ENOENT (No s
+uch file or directory)
[pid 15950] stat("/usr/bin/echddo", 0x7fffb62454b0) = -1 ENOENT (No su
+ch file or directory)
[pid 15950] stat("/sbin/echddo", 0x7fffb62454b0) = -1 ENOENT (No such 
+file or directory)
[pid 15950] stat("/bin/echddo", 0x7fffb62454b0) = -1 ENOENT (No such f
+ile or directory)
[pid 15950] write(2, "sh: ", 4)         = 4
[pid 15950] write(2, "echddo: not found", 17) = 17
[pid 15950] write(2, "\n", 1)           = 1
...

( cmd:  echddo arghh' 2>&1 )
...
[pid 15945] rt_sigaction(SIGTERM, NULL, {SIG_DFL}, 8) = 0
[pid 15945] rt_sigaction(SIGTERM, {SIG_DFL}, NULL, 8) = 0
[pid 15945] write(2, "sh: ", 4sh: )         = 4
[pid 15945] write(2, "Syntax error: Unterminated quote"..., 40Syntax e
+rror: Unterminated quoted string) = 40
[pid 15945] write(2, "\n", 1
...
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What shell are you using?  (bash v3.2.39 here)

Your version seems to be trying to find the binary for 'echddo' before having set up the redirection...