Investors & landlords

Turbo Tax is so confused about RSU.  I have discussed with several people who also agreed.  Assuming vested RSU is 100 shares, 40 of 100 shares were withheld for tax.  Also assuming $15 per share is the market fair value on vested date.   Therefore the  total proceeds is 100x$15=$1500.  This has been reflected as income in W2.  Following step by step on Turbo Tax, the cost base is 60x$15 = $900  the short gain = 1500-$900 =$600.   Is his right?  If so, final check has error since it requires additional lot about 60 share.