Entering Employee in Salary Slip Doesn't Always Update Designation or Department

I’ve been having an issue when creating a Salary Slip. Setting the employee sometimes doesn’t update either the department or the designation. I’ve only seen it when dealing with some newer employees I’ve created so I’m not sure if it is a bug. I’ve looked through the code to see where these two fields are being updated but wasn’t able to find it in the salary slip js. Could someone point me to the code?
So far I’ve solved it by using add_fetch so I know these employees have the correct information set. This might be a related issue: Designation is not updated on Salary Slip · Issue #4666 · frappe/erpnext · GitHub

cur_frm.add_fetch('employee', 'designation', 'designation');
cur_frm.add_fetch('employee', 'department', 'department');