This bug is simple to reproduce in all Qt4 and Qt5 versions.

Create a table with a column that has a default value set:

CREATE TABLE colors (
color varchar DEFAULT 'green'
);

Then use

QSqlRecord r = QSqlDatabase::record("colors")

to request an empty record. The default value in r.field("color").defaultValue() should be "green", but it is
"green':character varyin".

This is due to a bug in the Qt postgres plugin that extracts the
default value.

A test program is attached in qtbug.tgz. Additionally I added a simple patch
that fixes the bug. The patch was generated against Qt 5.2.1.