The reason is that once a joint return is filed (and the due date passes) then both spouses are equally liable for anything that was on the tax return. One spouse cannot remove that liability after the fact.
The only exceptions are if the joint return was not valid because the tax payers were not marred or forgery was involved or other factors that would invalidate the joint return . Having a joint return declared invalid is a complicated procedure with tons of paper work, buried in the IRM (manual), that usually takes a tax attorney to do.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
