Neutral particle oscillations / quantum number conservation

[Garlic]

Hello everyone,
Why don't neutral particle oscillations have to obey conservation of (quark) flavor quantum numbers, with the example of neutral Kaon oscillations?

 

[Orodruin]

Because weak interactions are not flavour diagonal. In general, you would expect mixing among particles whenever they have the same gauge quantum numbers unless there is a symmetry to forbid it.

 

[mfb]

Why should they? There is no conservation law for quark flavors, the weak interaction can change them. The oscillations happen via the weak interaction.

Edit: Too slow.