Forcing 2 Decimal Places on a String Property in Mobility

Summary

A field called "subtotal_markup_parts" has a regex configured, but the values are not constrained once the field is calculated

Content

Hello,

The customer has a string property called "Subtotal w/ Markup" [label = subtotal_markup_parts] which has a regex configured:
/^(?!.{8,})\d{1,6}(\.\d{1,2})?$/

The regex is supposed to force the value of this property to be limited to 2 decimal places, however it seems that since this property displays the calculation of two other properties, the regex doesn't work. See the below 3 screenshots:
 

subtotal_markup_parts is configured as so =  subtotal_markup_parts.png
name: Subtotal w/ Markup
label: subtotal_markup_parts