interrupt priority question？

my platform is CCS3.3, C6747, bios v5.41, code generation v6.11.
    my program like this:
 void INT4（）
 {
  sendData（）；
 }

 void INT14()
 {
  timerDeal（）；
 }

 ON C6747 platform，the INT4 is highest priority interrupt， but I find the fact when INT4
  interrupt service function execute，the INT14 can occurr which interrupt the function sendData（）
  cause my program work unnormal。
      INT4 is a GPIO external interrupt，while INT14 is DSP/BIOS system timer，interval 1MS，and
  interrupt service function configed with DSP/BIOS。
      why INT14 can interrupt INT4，low priority can interrupt Highest priority，who can tell me？