underscore split to alias

I am not sure this is a bug, but I was surprised by the following behaviour
in HEAD and 8.4.4 (instances built today, 2010.05.14):

Invalid (?) values like 123_456 are split before the underscore and interpreted as
123 as "456":

$ psql -p 6591 -d testdb -c "select 123_456, current_setting('server_version')"
_456 | current_setting
------+-----------------
123 | 9.0beta1
(1 row)

$ psql -p 6584 -d testdb -c "select 123_456, current_setting('server_version')"
_456 | current_setting
------+-----------------
123 | 8.4.4
(1 row)

Older versions (8.3 thru 7.4) all give an error:

$ psql -p 6583 -d testdb -c "select 123_456, current_setting('server_version')"
ERROR: syntax error at or near "_456"
LINE 1: select 123_456, current_setting('server_version')
^

The error given by the older servers seems justified. I assume
this is a bug and not a deliberate change?

thanks,

Erik Rijkers