Moe,

I've done the same thing on a project and had a simular thing occur.
Instead of a space (0x20) I had 0xFF. My problem was when the
timer finished the 10 bits in and re-enabled the Pin Interrupt line.
Any 1 to 0 transition since the last interrupt remained flaged.
Simply clear the Interrupt Flag before re-enabling the IRQ line.

CLR IE0 ; TCON.1
SETB EX0

Good luck.

J.