Unwanted Current in 8 Segment Display
I think what you are seeing is because your Output enable pin is always low so when you are shifting the bits especially the decimal point since it is the last one you are seeing the bit shifting through and lighting the segments as it shifts out. What I'd recommend is the drive the OE pin from the arduino in such way that the output is disable while updating the shift resister and then enable the output once this has been done to avoid seeing the bits shift through the register.