Please follow the general troubleshooting steps first:

• Ran brew update and retried your prior step?
• Ran brew doctor, fixed as many issues as possible and retried your prior step?
• If you're seeing permission errors tried running sudo chown -R $(whoami) $(brew --prefix)?

Bug reports:

After the recent upgrade of qt5 in homebrew, issues of the type Class SOMETHING is implemented in both my.app/Contents/Frameworks/QtCore.framework/Versions/5/QtCore and /usr/local/Cellar/qt5/5.6.1/lib/QtCore.framework/Versions/5/QtCore. One of the two will be used. Which one is undefined are not fixed by macdeployqt.

Normally one has to copy /usr/local/Cellar/qt5/$VERSION/plugins/ to my.app/Contents/PlugIns and run /usr/local/Cellar/qt5/$VERSION/bin/macdeployqt

I solved the problem by installing qt5 5.6.0:

brew -v install https://raw.githubusercontent.com/Homebrew/homebrew-core/7f5799fd2178001b715827e3a84e021923d357c2/Formula/qt5.rb

and running the steps described previously.

Has this something to do with the build in homebrew?. Please feel free to close this report if it is an issue related to the new qt5 version.

Thanks.