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most of extra key like this controlled by different software, I suggest you reinstall SW or driver for this keyboard
maybe this driver software can solved your issue, if your keyboard wireless comes from HP
http://h10025.www1.hp.com/ewfrf/wc/softwareDownloadIndex?softwareitem=ob-123643-1&cc=us&dlc=en&lc=en&os=4132&product=5259996&sw_lang=
but ask HP for the details answer