Do you want the solution or you want to know why? If you want to know why, you will have to check the IRS website.
Again, File Schedule C, SE for full amount, any deductions you have to take them on 2106 because taxpayer is NOT a statutory employee. These people are paid their salary and on top of that... they are paid the employer's share of social security. So, if they hire you and they say, "we are going to pay you $100K yearly but we are not going to withhold any taxes for you, so we are going to pay you $107,650 and you are responsible for all taxes"