Partitioned SUM() fails with expression

The following query works:

SELECT r1_1."store__id" AS "store__id", r1_1."region__id" AS "region__id",
    r1_1."fact_sales_sales_amt" AS "amount",
    SUM(r1_1."fact_sales_sales_amt") OVER (PARTITION BY r1_1."region__id") AS "gross_sales_sum"
FROM
(
    -- leaf_node(out, fact_sales)
    SELECT fact_sales."store_id" AS "store__id", dim_store."region_id" AS "region__id",
        SUM(fact_sales."sales_amt") AS "fact_sales_sales_amt", SUM(fact_sales."tax_amt") AS "fact_sales_tax_amt"
    FROM fact_sales
    JOIN dim_store
      ON dim_store.store_id = fact_sales.store_id
    JOIN max_dim_date
      ON max_dim_date.the_date = fact_sales.the_date
     AND (max_dim_date.the_month ILIKE 'january')
    GROUP BY fact_sales."store_id", dim_store."region_id"
) AS r1_1

But a partitioned sum() with an expression fails with a generic server error.

TIOStreamTransport.java:read:130:org.apache.thrift.transport.TTransportException: Socket is closed by peer.

SELECT r1_1."store__id" AS "store__id", r1_1."region__id" AS "region__id",
    r1_1."fact_sales_sales_amt" AS "amount",
    -- this causes the problem
    SUM(r1_1."fact_sales_sales_amt" - ABS(r1_1."fact_sales_tax_amt")) OVER (PARTITION BY r1_1."region__id") AS "net_sales_sum"
FROM
(
    -- leaf_node(out, fact_sales)
    SELECT fact_sales."store_id" AS "store__id", dim_store."region_id" AS "region__id",
        SUM(fact_sales."sales_amt") AS "fact_sales_sales_amt", SUM(fact_sales."tax_amt") AS "fact_sales_tax_amt"
    FROM fact_sales
    JOIN dim_store
      ON dim_store.store_id = fact_sales.store_id
    JOIN max_dim_date
      ON max_dim_date.the_date = fact_sales.the_date
     AND (max_dim_date.the_month ILIKE 'january')
    GROUP BY fact_sales."store_id", dim_store."region_id"
) AS r1_1

-Larry