IF ELSE vs CASE WHEN

Can someone explain why the first statement works, but the second one generates an error if myfunc() does not exist? 

1) if exists(select name from sysobjects where name = 'myfunc') select dbo.myfunc();else select 0;

2) select case when exists(select name from sysobjects where name = 'myfunc') then dbo.myfunc() else 0 end;

Generates this error if myfunc() does not exist, even though it should not be executing that case:

Cannot find either column "dbo" or the user-defined function or aggregate "dbo.myfunc", or the name is ambiguous.