Document input controls changes text dimension into number

Dear community,

Recently my company updated from 2016 SP2 to SP8. We encounter a problem in some of our reports, where we have a string variable (dimension) that can be changed via Document input control.

The options are custom, and are like 00, 01, 02 ect. However, if one of these options is selected, the dimension that stores the variable is changed from a text object into a number. How can this be avoided?