Office challenge: When an IF() returns FALSE, when it should return TRUE

This week, your challenge is to discover why a seemingly perfect IF() function returns the wrong result.

A user sends you a workbook with a simple IF() function that compares the text in two cells. If the two values are the same, the IF() function returns TRUE. When they don't match, the IF() function returns FALSE. Simple, right? It should be, but there's a fly in this one. Two cells (A4 and B4) contain the same text value, but the IF() function returns FALSE. Any idea what the culprit is?

There's more than one possibility, so we made the downloadable example available.