Website bug? I honestly doubt it. That leaves open the possibility that errors could go in favour of the passenger, and RYR unnecessarily lose money. That wouldn't be acceptable for any company. Besides, in this day and age there is no excuse for having online booking that isn't accurate.
I have to agree with Red Snake's "smoke and mirrors" comment. It's a shame that this taxes and charges thing is an issue at all because it certainly leaves a bad taste in the mouths of many, reduces confidence in the market in general, and certainly adds fuel to the fire against RYR for those who want it.
As I have posted here before, I have never trusted RYR on explanations for prices/charges etc. particulary when you look at their responses to advertising complaints in Ireland (see
www.asai.ie). But as Red Snake says, the total price is the total price. Once you come to the end of the online booking process, you see past the smoke and mirrors. If you don't like the fair, don't book it and look somewhere else. End of story really.