In Programmer mode (View -> Programmer) when Dec and Byte are selected the minimum value the calculator can accept is -128. It's tricky to enter that value but you can do by the following four key-presses: (1) (+/-) (2) (8). I said it's tricky as you can't type (1) (2) (8) (+/-) because 128 is greater than the maximum value of INT8 that is 127. While it's a bit inconvenience it can be worked around.
To reproduce the bug select Dec and Byte and type -128. Copy it to the clipboard via Edit -> Copy or Ctrl+C. Then paste it via Edit->Paste or Ctrl+V. What happens is -12 is pasted rather than -128, discarding the last digit.
|Last digit is discarded when -128 (INT8_MIN) is pasted.|
The effect is the same if you copy -128 in Notepad then paste it in Calculator.
While a beeping sound may be heard when pasting, nothing else warns you about the error. Those who muted the speaker may not notice the error. This is especially possible when the value is long in digits (INT64_MIN) and can be easily overlooked.
It's plausible that programmers use INT_MIN values in their calculations as these are commonly used when developing software.
Windows 8.1 is affected by this issue. Other versions are not verified but likely affected.
While this issue is most likely the limitation of the design some may find it embarrassing as a calculator has nothing else to do than to work with numbers without failure.
The issue found when I was recently working on my own calculator for Windows Phone. I realized I had to deal with many corner cases and I checked how these corner cases affect Windows Calculator.