polyglot idiot, or why blackbox testing isn't a cure-all

[trochee]

A coworker points out this dialogue on a Chinese help site.

In rough translation (thanks Babel Fish!):

Microsoft's bug!
This bug is in the Microsoft Windows calculator accessory (start > accessories > calculator). When you try 9216 divided by 96 and press the = button, the calculator doesn't respond! ! ! But 9,216 by 97, 98 all are actually normal.

Please explain this!

Dear reader, I encourage you to try it out for yourself! Join the QA revolution: you will see the same thing.

Amazingly, and unexpectedly*, I myself -- lowly dev that I am -- am able to reproduce this bug with the Linux utility xcalc and with Google.

*actually not unexpected at all. If you have a calculator that does not exhibit this bug, please let me know. Reverse Polish calculators need not apply. [Edit: or non-decimal calculators.]

[edit: Google is pretty smart, actually: here's light speed in furlongs per fortnight.]