<exec /> task does not put anything to console if output attribute is set to a filename.
This bug appears starting from 0.90 alpha release, and until the latest release 0.91-alpha2 at the moment.
My build scripts often use the behavior when nant puts it to console and logging output, I need to review the output even if is it put to sume file by output attribute, this file can be on some remote machine, it could be appended, etc.
So I have to patch your new releases with 0.86 code
to avoid changing all my build scripts to make them add output file content explicitly.