Suitable X-server version for version 5.1.12?

[VBoxer2]

Hi,

I'm running an up-to-date Debian Testing guest on an OS X host. The latest guest additions 5.1.12 that are shipped with VBox are installed. Since a few days I face the following issues:
- blocky artifacts from other host windows all over the guest screen. They disappear when I click the host window's close button and cancel the next Virtualbox dialogue window,
- copy-and-paste failures from guest to host though I activated the bidirectional clipboard.
I assume that the cause may be the guest's X-server. The guest has X-server.org 1.19 installed. Is this the right version for VBox 5.1.12 or another version required?

Thank you in advance.

[Perryg]

Post the guests log file ( as an attachment ). Right click on the guest in the Main Manager then click show log. Save and post as an attachment. Compress if it is too large to post.