In three words, Quark 6 sucks. The company had their heads lodged in the lower part of their collective torsos when they developed it and refused to support Unicode. (Their CEO was such a dork he even bragged about it.) As such, you can't expect non-Latin languages to reliably work in it.
Word has a reasonably good type engine. Native Cocoa applications work great with nearly all languages, of course. But not Quark 6.
Quark 7 might have reversed course. I'm not interested in their software these days, so I'm not sure.