Confused about app structure

[lc]

Actually, I have things working but am not clear why do they work.
Here's the setup:

3 projects
1. Data component (DataAuth) with connection, adapter and typed
dataset (DSAuthors). Two methods,
public DSAuthors OpenAuthors( )
public DSAuthors SaveAuthors( DSAuthors dsDelta )

2. Web service (WSAuthors) with two methods as well:
public DataAuth.DSAuthors GetAuthors()
public DataAuth.DSAuthors SaveAuthors( DataAuth.DSAuthors auth )

3. WinForms app (WinAuth) with two methods:
private void LoadAuthors() -> works as expected
{
WinAuth.refWSAuthors.svcAuth ws
= new WinAuth.refWSAuthors.svcAuth();
ws.Credentials = System.Net.CredentialCache.DefaultCredentials;
WinAuth.DSAuthors1.Merge( ws.GetAuthors() );
}

and
private void SaveAuthors()
{
WinAuth.refWSAuthors.svcAuth ws;
// DMAuthors.DSAuthors authChanges;
WinAuth.refWSAuthors.DSAuthors authChanges;

ws = new WinAuth.refWSAuthors.svcAuth();
ws.Credentials = System.Net.CredentialCache.DefaultCredentials;

authChanges = new WinAuth.refWSAuthors.DSAuthors();

authChanges.Merge( dsAuthors1.GetChanges() );
authChanges = ws.SaveAuthors( authChanges );
dsAuthors1.Merge( authChanges );
dsAuthors1.AcceptChanges();
}

Here's where I got confused: I would expect that a call to
ws.SaveAuthors, which is defined as "accept and return
DataAuth.DSAuthors" would indeed need a var of that type. However,
compiler wouldn't let anything through unless it's a type of
WinAuth.refWSAuthors1.DSAuthors. So instead of

DMAuthors.DSAuthors authChanges;
...
authChanges = ws.SaveAuthors( authChanges );

I had to use

WinAuth.refWSAuthors.DSAuthors authChanges;
...
authChanges = ws.SaveAuthors( authChanges );

The funniest thing of all is that everything works. I'm very much
newbie in .NET world and this is very confusing to me. Any help would
be highly appreciated.

TIA

lc