fork issue when lauching cygwin64 process from 32bit native app on Windows 10 TH2

Tue Dec 1 10:28:00 GMT 2015

After upgrading to Windows 10 TH2 (ver 1511, build 10586), any attempt
to launch a cygwin64 process from 32bit native app (for example,
C:\windows\syswow64\cmd.exe) *always* results in a fork error.

To be precise, I can execute 64bit bash.exe from 32bit cmd.exe.
However, this bash process never succeeds in forking a child (ls or
Also, I cannot launch 64bit mintty.exe from 32bit cmd.exe. It always
fails in a error dialog saying that:

mintty: could not detach from caller
Try '--help' for more information.

When launching from 64bit app, this issue doesn't happen.

Problem reports:
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