cell references lost after sorting

Does anyone know if this is an excel bug ?

I have a column H which is calculated by adding a number to the value in column F. This value is looked up from a table on another worksheet (locatietabel)

H2 =IF(F2="";"";F2+INDEX(locatietabel!$B$2:$AY$51;MATCH(overzicht!E2;locatietabel!$A$2:$A$51;0);MATCH(overzicht!G2;locatietabel!$B$1:$AY$1;0)))

Sorting the table alters the references in the formula (for example, by sorting, row 137 becomes row 2)

H2 =IF(F2="";"";F2+INDEX(locatietabel!$B$2:$AY$51;MATCH(overzicht!E137;locatietabel!$A$2:$A$51;0);MATCH(overzicht!G137;locatietabel!$B$1:$AY$1;0)))

I want to have the correct cells E2 and G2 instead of E137 and G137 after sorting. Does anybody have a solution for this ?

Thanks,

Gert