why does the ring tone on my motorola krzr play for 3 seconds and then swing

[Random]

to one of the standard ring tones? it's so weird; i loaded the song onto my memory card and set it as my ringtone for calls. but whenever i get a call, my cell phone will play the song for about 3 seconds and then switch ring tones to one of those horrible standard ring tones that come with the phone. of course, i want the song to play right on through.

any ideas would be very appreciated. thanks!