I'm the author of http://jhipster.github.io/ which is the generator your are referring to.
I have found your problem, it is indeed a bug in jpegtran-bin. I have updated all the dependencies in Grunt.js, and it should now work fine on Windows.
This will be commited in the next release (0.2.1), which should be out in a few hours.
You can also submit a bug at https://github.com/jhipster/generator-jhipster/issues