An icon in pbx is changed , need explanation

hi,
i want to ask , why sometimes the icon of pbx is changed and become sip/extention number

i mean that in pbx , the defualt is extentionnumber:name
as you see form image
100:manager , and thats usual

but from image , note that my extention 108 changed to sip/108 !!!

my question is why this happened ??