Just a few wild guesses....

You have STDIN as undefined, I don't know if IPC3 likes that, it may want a 0 (true or false); and it may have to be a dummy filehandle in there to keep STDIN open for some reason.

my $pid = open3(  \*WRITE,  \*READ, 0,  "bc");
     #if \*ERROR is false, STDERR is sent to STDOUT
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you may want to look at the examples in "perldoc -q stderr" and see how they use gensym and IO modules.

If you don't need STDIN to the spawned program, why even use IPC::Open3? A plain piped open with 2>&1 should work, unless you absolutely need to separate STDOUT from STDERR.