Ajax requests are called serially using only one channel (Channel busy - postponing...)

I have several lazy load panel that load DynamicImageResource objects. They are always loaded in serial mode. These are the debug messages:

INFO: Initiating Ajax GET request on ../?wicket:interface=:3:tabpanel:panel:app_graph_panel:1:graph::IBehaviorListener:0:1&random=0.7774967316771
INFO: Invoking pre-call handler(s)...
INFO: Channel busy - postponing...
INFO: Channel busy - postponing...
INFO: Channel busy - postponing...
INFO: Channel busy - postponing...
INFO: Channel busy - postponing...
INFO: Channel busy - postponing...
INFO: Channel busy - postponing...
INFO: Channel busy - postponing...
INFO: Channel busy - postponing...
INFO: Received ajax response (2665 characters)

After checking the code, it seems that every Ajax code in Wicket does not specify the channel when calling wicketAjaxGet. By doing that, all the requests end up in the default queue, being executed serially.