it's not odd or curious.. it's normal. You're working with digital signal on analog by default I/o.

Open the PIC16F88 datasheet and discover the Analog section... section 12.0 and 13.0.

Now you need to disable the analog stuff
section 12.0 register 12-1 ANSEL:
ANSEL=0 ' set all related i/o to digital mode

Section 13.0 register 13-1 CMCON (and figure 13-1)
CMCON=7 ' Disable analog comparator

ok those comparator are already disabled by add the line just for safety sake

So add
ANSEL=0
CMCON=7
at the top of your code.
About now?