Replacement path formula variable replaced from a variable used in a formula-if else

hello BW experts.

I have a date type char ZDT_TYP and I have created two input ready variables on it. ZDT_TYP has text maintained in it like 1..complaint date, 2..incoming date.I now have created a formula variable ..zstart_date which will be replaced by variable created on ZDT_TYP with variable key.So when I select 1 in Start Date in selection, formula variable start date will get 1..Now i use this formula variable in a boolean expression

If Start date ==1 * complaint date(char in cube).. This does not give the result.However when I use formula variable input ready .and I directly input 1 the boolean expression reads correctly and the formula shows the complaint dates.

can we not use formula variable replaced with a variable key not give results in Boolean.

Thanks.