select avg() and sum() returns false value

Christoph Lorenz (Christoph_Lorenz(at)gmx(dot)de) reports a bug with a severity of 2
The lower the number the more severe it is.

Short Description
select avg() and sum() returns false value

Long Description
I don't know, if it's my fault, but when I sum up several thousands
of positive entries in a column (the column is an int2 field), I get a negative(!) value.

Sample Code
CREATE TABLE recording (
[...]
time int2 DEFAULT NULL,
[...]
);

select time from recording returns only positive values, like time
------
277
159
192
183
184
178
180
207
243
194
203
182
277
159
192
183
184
178
180
207
243
194
203
182
229
229

and when I sum it up, the following happens (remember, there are really no negative values in my database):

mmusic2=# select sum(time) from recording;
sum
--------
-12491
(1 row)

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