When you bottle prime (add more sugar to create carbonation) the sugar will ferment and leave sediment on the bottle bottom, to prevent it clouding the beer/wine/cider you need to let it sit in the fridge for a month (this will depend on the yeast) to allow it to compact and stick to the bottle a bit. When you open a bottle and start pouring it you pretty much need to pour the lot in one go or else the beer/wine/cider will swill back over the compacted yeast which will then cloud it, the clouding is made worse due to the high fizz of wine, it isn't an issue if you don't care about it but with bubbly wine it doesn't look good. You could use something like a sodastream to force carbonate the wine using there bottles, that way at least you get sparkling clear wine though this isn't something i have ever tried.