According to Tax Prof, in the case of Jellen v. Commissioner, the U.S. tax court ruled that unclear instructions from the IRS is not a valid excuse for a taxpayers mistake. Check out a quote from the ruling below.
Petitioner's only argument is that respondent's instructions and guidance to taxpayers as to the taxability of Social Security benefits are confusing and unclear and therefore that the Social Security disability benefits he received in 2004 and 2005 should not be subject to taxation under section 86(a).