Balloon bug? (changes b when b--)

I have test code that looks like this in insight:

  	1	int main (void)
-	2	{
-	3		int a = 0;
-	4		int b = 10;
  	5	
-	6		while (b--)
  	7		{
-	8			a = a + 1;
  	9		}
  	10		/* should be 10 */
-	11		return a;
-       12       }

It appeared that "b" was sometimes decrementing by more than 1 as I 
stepped through. So sometimes "a" would result in less than 10. I found 
that the balloon inspection (by holding the mouse over the variable) was 
causing b to decrement if I touched the --. I don't think I have ever 
seen this before using insight. This is version 6.8.

-gene