Windows 10 64 bit, 980TI
Broken: Recent master (cb1cb63)
Short description of error
When saving a render to the OpenEXR format, all the codecs (except the first two) produce files of exactly the same size. This makes me think that none of them are actually doing any compression.
I tested both RGB and RGBA, Float (Half) and Float (Full) - the Codec option still makes no difference.
 DWAB and DWAA seem to be the only codecs that produce different size files.
Exact steps for others to reproduce the error
Save any image (e.g. a render of the default cube) several times using the OpenEXR format, and set the Codec to something different each time.
Here's a zip of my own test: