Gannt task bar % complete visual wipes out formula and forces static text

I have made a column with % complete based on todays date (using a formula) and it works great. I want to use this dynamic information to display the % complete on the Gannt task bars, but when I activate that setting, the formula gets wiped out (and forced to static text format). I can figure out a work around, but I would much rather use the formula column to display the % complete as it changes over time. Can this be done?