General power of attorney

In the year 2004, Mrs. A executed General Power of attorney in favour of her husband citing that she owns certain properties and she herself being female and unable to do various acts and authorising attorney to sell property on her behalf. Interestingly, after four years of execution of GPA, a property was purchased in the name of Mrs. A and same was sold in the year 2012 by Mr. B on the strength of GPA executed in year 2004. The question is whether GPA executed in year 2004 for the purpose of managing/selling properties will hold good for property purchased at subsequent stage.? If not what remedies are available to person who had purchased property on the basis of said GPA.?