How to enter tax liability?

[Jack Tannery]

I am new to gnucash and
trying to enter my last three years' business accounts into the programme and
produce sensible reports.

I wish to enter my
income tax liability for 2011 (which was paid in 2012) as a liability
to appear on the 2011 balance sheet. How do I do this? I tried
creating a new account under LIABILITIES called 'Business Income Tax'
and adding a liability here of the total that I owe dated 31/12/2011,
which I was going to later pay off from my bank account in 2012.
However for some reason GnuCash isn't letting me do this (it inserts
a second entry below, offsetting it). 

What am I missing?

JT.