Hi,

I do agree with Michael that microcontroller programs never end. The END in your code simply tells the assembler that the work is done. It is not an instruction to the micro that it can stop working. Every instruction will be followed by an other instruction. If you don't supply the instructions yourself, the micro will interpret the next byte fetched from memory as it's next instruction. This continues until the program counter rolls over from FFFF to 0000 where the program will start all over again.
If in your application the processor is ready at a given point, simply add an infinite loop like JMP $ to avoid the above problem.

Happy programming.