I didn't do any specific testing, but Samba 4.0.0rc4 works just fine with Ajenti on multiple servers I supervise.

Please remove ProxyRequests and ProxyPreserveHost, it doesn't work for me with those either.

Can you please post your updated configuration?

I had success with this config (note the proxypass order):

<VirtualHost *:82>

SSLProxyEngine On
SSLProxyCheckPeerCN Off
SSLProxyCheckPeerExpire Off

RequestHeader set Origin https://localhost:8000

ProxyPass /ajenti https://localhost:8000/
ProxyPass /ajenti:socket/1/websocket/ wss://localhost:8000/ajenti:socket/1/websocket/
ProxyPassMatch ^/(ajenti:.*)$ https://localhost:8000/$1
ProxyPassReverse /ajenti /

</VirtualHost>

Sorry, I didn't notice that you were using SSL. In this case, you need to use wss:// websocket URL. 
I'm not sure if this will resolve your problem fully - I'll set up your configuration at my side for testing later today.

Does it work if you comment out ws:// ProxyPass?

Could you please check /var/log/ajenti/ajenti.log?

Actually I messed up the plugin list, not the versions. proxy_wstunnel should only be used with 2.4+.
I see that you use HTTPS between Apache and Ajenti, but that just doesn't make sense (unless Ajenti is also available directly from outside, which doesn't make sense as well with Apache). I would suggest to make Ajenti listen on 127.0.0.1:8000 instead, without SSL.

http://munin-monitoring.org/wiki/Documentation , and then use the configured URL in Ajenti.

Fix committed