In Vivado or PlanAhead, when I open the LUT equation box for a LUT4 with INIT value = 16'hABFB, it shows "O=I0".
The truth table in the cell properties correctly shows the output values but the equation (O=I0) for the output does not match the truth table.
In the first line of the truth table, "0000" (O= 1) <> (I0 = 0).
The correct value that should be shown in the LUT equation box is "O = (I0 + (I2 * !I3) + (!I1 * !I2))".
This is only a display issue and will not affect LUT4's logic function.
This issue is fixed in the 2015.1 release of Vivado Design Suite.