Why does MySQL unix time stop short of the 32 bit unsigned integer limit?

mysql> SELECT FROM_UNIXTIME(2145916799), FROM_UNIXTIME(2145916800), POW(2,32-1)-1, 2145916799 - POW(2,32-1)-1;
+---------------------------+---------------------------+---------------+----------------------------+
| FROM_UNIXTIME(2145916799) | FROM_UNIXTIME(2145916800) | POW(2,32-1)-1 | 2145916799 - POW(2,32-1)-1 |
+---------------------------+---------------------------+---------------+----------------------------+
| 2037-12-31 18:59:59       | NULL                      |    2147483647 |                   -1566850 | 
+---------------------------+---------------------------+---------------+----------------------------+
1 row in set (0.00 sec)

mysql> 

The first field is the highest possible value I can give to FROM_UNIXTIME. The next field is that value plus one which returns NULL. The third field is the highest possible value for an unsigned 32 bit int. The final value is the difference between the highest possible UNIXTIME and the highest possible int which is a little over 18 days worth of seconds. It appears that it stops at the end of 2037 in the local timezone. Any ideas why? Is that a natural breaking point in one of the calculations? Is that just an arbitrary limit in mysqld?