Like many things in the PI System, AFEnumerationValues are case-insensitive. Units of measure are too, and this can naturally create a dilemma when, say, working with megabits (Mb) and megabytes (MB) or milliwatts (mW) and megawatts (MW). In the case of those units of measure, the solutions I've seen and liked were to lengthen one or both of the abbreviations: Mbits and/or MBytes.
It's not perfect, but could that workaround suffice for you?
Thanks for the information. I will make it work.