I upgraded my Spket installation to 1.6.20, I'm using the eclipse plugin with an eclipse 3.6 (I had the same problem in 3.7).
After upgrading, code completion will only give me direct descendants of a given object. For example if I type "Ext." I will get FormPanel, but not form (which gives access to ComboBox etc).
I have the same kind of problem with the jsb2 I am using for my own components, although some namespaces seem to be recognized.
The version I am upgrading from is 1.6.18, everything was fully functioning then.
I can provide you with more info if you need.