strange update behavior

I did encounter a quite strange behavior during update which I did not
understand:

The following query updated table parcelle with only one entry for all rows:

update cadastre.parcelle

set code_unique = t2.code_unique from

cadastre.parcelle t1, cadastre.propriete t2

where t1.uoid = t2.uoidparcelle;

the next update query behaved as expected :

update cadastre.parcelle

set code_unique = t2.code_unique from

cadastre.parcelle t1, cadastre.propriete t2

where parcelle.uoid = t2.uoidparcelle;

Why do i have to reference table parcelle in the where clause?