I think the issue outlined in this question PostgreSQL default values in QGIS 2.8.1 and ticket #12391 is not fully solved yet. Negative numeric values, and dates are not used by QGIS 2.8.2 correctly. 2.6 works.
Example:ALTER TABLE bla ALTER COLUMN vres SET DEFAULT -32768.0; => shows up as "vres double precision NOT NULL DEFAULT (-32768.0)" in pgadmin
ALTER TABLE bla ALTER COLUMN startvalid SET DEFAULT '2001-01-01'::date; => stvalid date NOT NULL DEFAULT '2001-01-01'::date,
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Example:ALTER TABLE bla ALTER COLUMN vres SET DEFAULT -32768.0; => shows up as "vres double precision NOT NULL DEFAULT (-32768.0)" in pgadmin
ALTER TABLE bla ALTER COLUMN startvalid SET DEFAULT '2001-01-01'::date; => stvalid date NOT NULL DEFAULT '2001-01-01'::date,
أكثر...