Assigning variable value in right behalf of pipeline has no effect

[xandrous]

Hi, bash developers!

I've noticed strange bash behaviour. If I assign variable value in
right behalf of pipeline it has no effect. Just try to execute:

XXX=10; { XXX=20; } | read; echo $XXX

XXX=10; { XXX=20; }; echo $XXX

I suppose both of them should output  '20' but the first one outputs
'10'. Is it feature of bug?

This behaviour is the same for at least following bash versions: 2.05,
3.0.16 and the recent 3.2.