Solved! Go to Solution.
The simplest way to approach this would be to change how the calculated field is calculating.
Because I have no idea if your Calculated Control is actually hooked up to a Column, I've configured it as if it is linked to a Single Line Text Column.
While the formula might change slightly to meet your own needs, the configuration of the Control is the important part. I have highlighted the important part.
The Formula is as follows:
Configuring your control in this way means that it will ONLY grab the current user when the Form Mode is set to New, and will simply re-use the value of the control in any other mode, resulting in a one-time population.
I hope that this helps.