This error can be demonstrated by entering Pi (3.141592654) manually, instead of using the Pi button -- you will get the correct answer each time. Therefore, this error only shows up when you use the Pi button.
So, be sure to read up on this bug from the tipsters website before you use the calculator for anything too important.
Update: Reader Vineet writes in the comments to note that he believes this behavior is typical of stack-based calculators and should be considered more of an operator-expectations issue than a true bug. Dr. Drang responds (with a little bit of attitude) to disagree, maintaining that the behavior is a legitimate bug.
Thanks for the tip, Dr. Drang!
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