[Fixed] Hide

[micheus]

I don't see any bug here. What I didn't understand?

I select all faces from one object (it does not matter combined with others or separated) and use option 'Hide' - is there any option to restore the hidden faces? otherwise it works like 'Delete'

Not really as a 'Delete'. By doing that, it acts the same as you were in Body selection mode (with the whole object selected) and use the Hide object option (or the eye icon in the Geometry graph). So, to bring it back just use that option or the menu Select->Unhide all objects.

I assume 'Hide' has only functionality to limited faces from one object...

In this case you will get only the selected faces hidden. To unhide them you will need to select the surrounding faces you can see and use Hide with [RMB] option.
When we hide a lot of faces, show them back can be laborious. So, I have to say that I would like to have an option to show all the hidden faces in that object - all at once.