This is true of all disputed areas, regardless of country. In official statements and official viewpoints they are not considered disputed at all (to the point of all other claims being ignored), however in practice they are recognized as disputed for the purposes of practical military strategy.
And the strategy changes over time. Like when they backed off in the SCS, or when India backed off in Donglang, that gives China more room to set up more permanent military facilities, such as bases in the SCS and garrisons in Donglang.
Officially these areas are not disputed. In practice however, it would be foolish to ignore the ground realities when coming up with tactics or strategy. Otherwise, for example, India would just casually start building military bases in Aksai Chin, or Russia would conduct official military exercises in Eastern Ukraine. But obviously these things don't happen.