p-nitrophenol and sodium bicarbonate test

I was doing an experiment in lab and found that about one-third of p-nitrophenol dissolved in $\ce{NaHCO3}$ solution with liberation of $\ce{CO2}$ in small amount. This is contradictory to what most textbooks say. I was surprised as p-nitrophenol is less acidic than carbonic acid yet it gave positive $\ce{NaHCO3}$ test.


Can anyone give any possible explanation? I thought that one reason maybe that since their $\mathrm{pK}\_\mathrm a$ differ by about $1$, the reaction maybe in equilibrium to a significant extent, but this kind of thing isn't mentioned anywhere. 


