After installing new Extjs 4.2, I found that the "save" method of a model stops to work.
I found a minor difference between "buildUrl" in this version:
if (me.appendId && id)
if (me.appendId && (id != null))
This is in the "Ext.data.proxy.Rest" definition object.
The bug results in a malformed url like: /posts/.json instead of /posts.json