#unique not summing up correctly based on order of events

[dakotahNorth]

@unique is working differently depending on the sequence of events.

Given the following epl:

create schema StockTick(security string, price double);
create schema OrderEvent (orderId int, trader string, symbol string, strategy string, 
quantity double);

select orderId, trader, symbol, strategy, sum(quantity) 
from OrderEvent#unique(orderId) as o
full outer join StockTick#lastevent as t 
on o.symbol = t.security
group by trader, symbol, strategy

The following events:

StockTick={security='IBM', price=99}
OrderEvent={orderID=1, trader="A", symbol='IBM', strategy="VWAP", quantity=10}
StockTick={security='IBM', price=99}

correctly provides the sum as sum(quantity)=10.0.

But if the StockTick did not happen first:

OrderEvent={orderID=1, trader="A", symbol='IBM', strategy="VWAP", quantity=10}
StockTick={security='IBM', price=99}

I still expected the value of quantity to be 10. But in this case it is sum(quantity)=20.0!!

Why is #unique(field) not being adhered to and what is needed in the query for the output to be unique on orderId for both cases?

The following set of events is also available to run on Esper Notebook
https://notebook.esperonline.net/#/notebook/2HE9662E6

[bernhardttom]

Checked the docs on aggregations with joins? Is not the same as relational