The letter ζ does sound a bit awkward in some sentences. We have gotten reports about ζ sounding like χ, which is true. It seems like it's happing for words that end in -ίζει and in this case, -ύζι.
Sound is not something we (we as in, the Greek team) can tamper with. We just hope it will get fixed in the future, of with the release of the new tree. ^.^