Not sure on the debouncing bit. Sounds like you have short duration spikes of noise but would need an o'scope to check. Some sort of filtering, ferrite beads or capacitors for example might sort it out but I haven't the experience with line receivers to advise you.

We've discussed opto-couplers at length in the past (wasn't Doddy involved?) and I have been experimenting with a Long Bendy Optical Coupler (LBOC) recently but that will be for another thread.

Kit