Flex database - HTTP call collision? - web-services

Question

I have a Flex application for AIR. I fetch some data from a JSON-RPC web service through the mx.rpc.http.HTTPService class. I make all the calls asynchronously. When the results return I process them and put the data into an SQLite database through the flash.data.SQLConnection. This means quite some updates per web service calls so every callback starts a transaction, does the updates and then commits.
According to my debug console tracing I see two kinds of behaviour: either a callback successfully begins a transaction, calls the transaction event handler function, does all the updates, commits and then the next web service call returns. Or a callback successfully begins a transaction and as the next web service call returns (without trying to start a new transaction yet) the previous callback just... ceases to exist even before the callback of the beginning of the transaction.
Is that a bug in Flex? Or in AIR? Or in ActionScript? Or in the specific components? Do I do something wrong? Is this just my misunderstanding? (I'm just trying my wings in Flex, I don't really know what to expect from the system or how to handle this situation.)
Some code from my database manager class
public function beginTransaction(handler:Function):void {
// The calls are all fine up to this point
conn.begin(SQLTransactionLockType.DEFERRED, new Responder(handler, OnError));
// Begin is always called first. If another web service call doesn't come
// back up to this point then it won't until I call commit in an other
// function.
trace("this always runs yet");
// But if another call comes back just after begin is called then handler
// won't get called. Even though the previous trace still will.
}
My web service call
public function getWSCall(url:String, method:String, param:Object,
handler:Function):void
{
var http:HTTPService = new HTTPService();
http.addEventListener(FaultEvent.FAULT, JsonError);
http.addEventListener(ResultEvent.RESULT, handler);
http.url = url;
http.method = "POST";
http.contentType = "application/json";
var params:Object = {};
params.jsonrpc = "2.0";
params.method = method;
if (param !== null)
params.params = param;
params.id = method;
var json:String = JSON.stringify(params);
trace (url + " " + json);
http.send(json);
}
And an example of how I call it
JsonConnector.instance.getWSCall(WSConstants.GET_DATA_URL,
WSConstants.GET_DATA_METHOD, param, getDataCompleted);
And in the getDataCompleted after some rearrangement I call my database manager class where I finally begin the transaction:
dbConnector.Open(key, opened);
function opened(event:SQLEvent):void
{
if(event.type == SQLEvent.OPEN) {
dbConnector.beginTransaction(onBegin);
}
}