Can imputed income be taxed and also be deducted from your paycheck as a post-tax deduction?

I added my domestic partner to my health insurance earlier this year.  I understand that the Fair Market Value of my employer's contribution to the health plan is a taxable benefit to me.  I also understand that the bi-weekly contribution I have to make to the insurance plan is a post-tax deduction to me.  However, my employer is also deducting the FMV  from my net pay.  For example:

Gross Pay:  $1000

Non-Taxed Deductions:  $100

Value of Employer Paid Insurance on DP: $175.00

New Taxable Income: $1075

Taxes: $232

After Tax DP Insurance Premium: $75.00

After Tax Taxable Benefits - $175.00

Net Pay: $593.00

I can't seem to get a straight answer from my HR or payroll department.  But something seems off to me and I can't seem to quite understand what's happening.