[enesunal]

... or show an error indication to user when things are mangled.

Never seen an out-of-sync error message in any application except for multiplayer apps/games.

[TeMPOraL]

Usually, you can just force a resync instead. Refresh button is needed for the situations when your application doesn't know its state is wrong, but the user does - which does happen whenever your app is displaying the state of a shared resource it doesn't own, like files on disk.