Transient Disk Usage Higher In 7.2 ?

Dear list,

I have a customer who is testing 7.2 before upgrading (from 7.1.3)

They are getting errors like :

cannot extend tablename - No space left on device check free disk space
or 
write to hashjoin temp file failed

However when they attempt the same query with a 7.1.3 installation (On
the same machine), they do not get these.
(I dont know how different the query plans are between the 7.1 and 7.2
tests... see below)

I am informed that there is "quite a bit" of free disk on the
machine.(no numbers I am afraid... I am going in to have a look on
Thursday).

Is there an "expectation" that 7.2 will use temp space more aggressively
than 7.1 ?

(They are using a vanilla Mandrake Linux - either 8.0 or 8.1...)

regards and apologies about the lack of specifics  :-(....

Mark