I am having two problems with Opus 11.5 X64 (Win 7 Pro) though they have been present at least through recent BETAs as well:
When DO opens a lister, if one of the panes was last connected to a network resource (eg another machine) and that resource has now left the network, instead of handling that gracefully, Opus just hangs. Sometimes it clears after 2 or 3 minutes, sometimes the hang is indefinite.
The folder tree these days seems very slow to reflect changes in directories. For example, a deleted directory may continue to show in the folder tree for a long time (even 30 minutes) after deletion when the lister pane has long updated. The tree continues to show the obsolete directory even through an F5 refresh.
Both these issues seem to be more due to DO than the operating system as Win Explore can be opened and shows proper info even whilst DO is misbehaving.