eval is not trapping the failed open3 call as you expect. Trim your code down to this:

[bmc@hacked lib]$ perl -MIPC::Open3 -e 'eval {$pid = open3(*IN, *OUT, 
+*ERR, @ARGV);}; print "ACK $@\n" if ($@);' asdf
[bmc@hacked lib]$
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Note that ack isn't printed. eval is working as expected as you can see when you call the same code with no args:

[bmc@hacked lib]$ perl -MIPC::Open3 -e 'eval {$pid = open3(*IN, *OUT, 
+*ERR, @ARGV);}; print "ACK $@\n" if ($@);'     
ACK open3(*main::IN, *main::OUT, *main::ERR): not enough arguments at 
+-e line 1
[bmc@hacked lib]$
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