Why does integer overflow work differently inside of if statement conditional?

In the following code, x and y are int32_t variables. In this simplified example, they always differ by 1. When they span the int32_t overflow boundary (0x7FFFFFFF, the max 2's compliment 32-bit positive number, to 0x80000000, the largest magnitude negative number), subtracting them seems to give different results when it is done inside the conditional of the if statement (Method 1) than it does if the result is stored in a temporary variable (Method 2). Why don't they give the same result?

I would think that subtracting two int32_t variables would yield a result of type int32_t, so using a temporary of that type shouldn't change anything. I tried explicitly typecasting inside the if statement conditional; that didn't change anything. FWIW, Method 2 gives the result I would expect.

The code:

int32_t x = (0x80000000 - 3);

int i;
for( i = 0; i < 5; ++i )
{
    int32_t y = x + 1;      // this may cause rollover from 0x7fffffff (positive) to 0x80000000 (negative)

    UARTprintf("\n" "x = 0x%08X, y = 0x%08X", x, y );

    if( ( y - x ) >= 1 )            // Method 1
        UARTprintf(" - true ");
    else
        UARTprintf(" - FALSE");

    int32_t z = ( y - x );          // Method 2
    if( ( z ) >= 1 )
        UARTprintf(" - true ");
    else
        UARTprintf(" - false");

    ++x;
}

Output:

x = 0x7ffffffd, y = 0x7ffffffe - true  - true
x = 0x7ffffffe, y = 0x7fffffff - true  - true
x = 0x7fffffff, y = 0x80000000 - FALSE - true
x = 0x80000000, y = 0x80000001 - true  - true
x = 0x80000001, y = 0x80000002 - true  - true