>> have @action and @actionListener any sense for group? it may be in case groups

>> are selectable, but they are not

Groups with selectable=true should be selectable. And even if group is non-selectable, action event makes sense as duplicate to toggle event.

>> @bubbleSelection / @expandSingle - should be possible to be define it on level of group?

>> I think this is attribute which needs to be defined on the level of panelMenu, not group/item

Agree, on that.

>> @bypassUpdates / @immediate - haven't sense since group toggling

>> should go through whole lifecycle

Both make sense. bypassUpdates should direct component to foollow shorter lifecycle, and immediate controls when events are delivered.

>> contains @selectable attribute, but it seems group can't be selected

Why?

>> contains @leftIcon / @rightIcon attributes which haven't any effect

Please report JIRA issue.

>> contains @leftIconClass  @rightIconClass which are working, but there are no equivalents for panelMenuGroup or panelMenu

>> components - should be removed or defined on all levels?

Why not, let's add them. Please create JIRA issue.

>> 7. when you disable group in expanded state, the group can't be collapsed but the items inside the group are still visible

IMO this is correct behavior.

>> 8. group has no "expanded" attribute to switch state on the server-side

It should be there, please create JIRA issue.