How to make MCLRE in CONFIG3 word work in PIC18F using MPLABX XC8
It is a bug in XC8.

As a workaround you can edit 18f14k50.cfgdata in C:\Program Files (x86)\Microchip\xc8\v1.01\dat\cfgdata\. Just above line with CWORD:300005:88:88:CONFIG3H add new line CWORD:300004:00:00:CONFIG3L.

Full post at http://www.jmedved.com/2012/08/elusive-config3h-setting/.