Problem with custom aggregates and record pseudo-type

I created special custom aggregate function to append arrays defined as:
CREATE AGGREGATE array_accum (anyarray)
(
sfunc = array_cat,
stype = anyarray,
initcond = '{}'
);

On arrays of common types it work without any problems:
SELECT array_accum(i) from (values (ARRAY[1,2]), (ARRAY[3,4])) as t(i);
array_accum
-------------
{1,2,3,4}
(1 row)

However once I try use it with record[] type I get an error:
SELECT array_accum(i) from (values (ARRAY[row(1,2),row(2,3)]),
(ARRAY[row(1,2),row(2,3)])) as t(i);
ERROR: cannot concatenate incompatible arrays
DETAIL: Arrays with element types record[] and record are not compatible
for concatenation.

The base function of the aggregate:
array_cat work with record[] without any complains:
SELECT array_cat(ARRAY[row(1,2),row(2,3)], ARRAY[row(1,2),row(2,3)]);
array_cat
-----------------------------------
{"(1,2)","(2,3)","(1,2)","(2,3)"}

What I doing wrong? Or how to create correct version of such aggregate
function?

--
Maxim Boguk
Senior Postgresql DBA.

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