Can't see whole screen (with WIndow 8.1 server)

[senesi]

Using UltraVNC Server 1.0.2 on Window8.1 and Vinagre on Ubuntu as a viewer, I have these issues :
- the lower and rightmost part of the remote screen do not show on the viewer (they are no scroll bar); hence, the task bar do not show
- the cursor is not well located ; the mismatch seems to be consistent with the amount of screen height/width which is missing
- screen refresh is at least slow, and eventually fails

All that happens whatever the choice of viewer scaling option

When configuring a scaling different than 1/1 on the server, I get a black screen on the viewer

The problems also occurs, with slight changes, when using a Windows 8.1 client (the one delivered with the same install package as server 1.0.2)

Thanks for any help