I've played with some MessageHandlers and found that if you specify order as follow

[MessageHandler(order="999")]
public function handler1(msg:Message):void
{
...
}

[MessageHandler(order="1900")]
public function handler2(msg:Message):void
{
...
}

than call order is 1900,999. This corresponds to flash array sortOn behaviour because by default Array sort occurs using string representation of field. You use this code

function Processor (receivers:Array, handler:Function, async:Boolean = true, handleErrors:Boolean = true) {
this.receivers = receivers;
this.handler = handler;
this.async = async;
this.handleErrors = handleErrors;
receivers.sortOn("order");
}

in org.spicefactory.parsley.core.messaging.impl.Processor class.

But order field is the numeric one, so you probably should use

receivers.sortOn("order", Array.NUMERIC);

This affects all places of code there you use such sorting.