FloatingActionButton, square button below API level 17

This is known by Google and will be fix soon in the next version of the Design Support Library, see this issue: FAB Appears as a square on API 16. It should only concern API 16.

The workaround, proposed in the same thread, is to add app:borderWidth="0dp" to your FAB.

Finally the issue has been fixed in the new release

  compile 'com.android.support:design:22.2.1'

this will solve the square layout issue in API 16. FAB performs well if you place it inside Coordinate Layout. Check out https://code.google.com/p/android/issues/list?can=1&q=label:Version-22.2.1 for issues and fixes in new version.

Released version 22.2.1 This release contains bug fixes related to FAB

https://code.google.com/p/android/issues/detail?id=175067

Change your gradle

compile 'com.android.support:design:22.2.1'

Install support repository revision 16. So you can avoid the workaround [app:borderWidth="0dp"]