Deductions & credits

from iRS pub 526 maybe this is the reason

  4. Contributions of capital gain property subject to the limit based on 30% of AGI. Deduct the contributions that don’t exceed the smaller of:
a. 30% of your AGI, or
b. 50% of your AGI minus your contributions subject to the limits based on 60% or 50% of AGI (other than    qualified conservation contributions).