Thank you for your message!
This bug is not as weird as you think. It is a simple memory problem. If you are low on memory or you want to play a big song (Just check the debug log for its size).
Anyway thank you for posting it here, even if it is already known. Try to ensure that as much RAM is available as possible to decrease this bug. I may fix it one day if I find enough time to code a workaround!
In the near future I will release a grooveshark(tm).com downloader for windows mobile
SciLor
PS:
The software's name is "SciLor's GrooveMobile" it is just based on Groovefish!