Strange behavior of the random() function

[r . zharkov]

Hello,
Can anybody explain me that strange behavior?

 select random() as "rnd", random() as "rnd1", random() as "rnd2"
 from generate_series( 1, 5 );
 ---
 0.948556384071708      0.769186236895621       0.381390900816768
 0.684488877654076      0.594888080842793       0.214444123208523
 0.668408528901637      0.452859566546977       0.924952184315771

All of the values are different.

 select random() as "rnd", random() as "rnd1", random() as "rnd2"
 from generate_series( 1, 3 )
 order by random();
 ---
 0.166236794553697      0.166236794553697       0.166236794553697
 0.629051928408444      0.629051928408444       0.629051928408444
 0.698161978274584      0.698161978274584       0.698161978274584

All values in any row are the same.

 select random() as "rnd", random() as "rnd1", random() as "rnd2"
 from generate_series( 1, 3 )
 order by random() || 'test';
 ---
 0.569052047561854      0.531697370111942       0.338135569822043
 0.880468992516398      0.172520748339593       0.0296505615115166
 0.862012444529682      0.119546371512115       0.21626165881753

All of the values are different again.

Is it a bug?