greedy or not? regexps...

Hi,
I am trying to understand the function substring.

Here:
select SUBSTRING(cit1.summary, '=([0-9]*)') from cms_items cit1
where cit1.summary ~* '.*linkadministration.*[0-9]*';

gives me two empty strings and

select SUBSTRING(cit1.summary, '=([0-9]{1,10})') from cms_items cit1
where cit1.summary ~* '.*linkadministration.*[0-9]*';

gives me the right values.

However, bizarrely,

select SUBSTRING(ban1.url_id, '=([0-9]*)')
from banner ban1
where ban1.url_id ~* '.*linkadministration.*[0-9]*';

select SUBSTRING(ban1.url_id, '=([0-9]{1,10})')
from banner ban1
where ban1.url_id ~* '.*linkadministration.*[0-9]*';

Both give me the same result!!! The difference being that in case two
the numbers I am catching are at the end of the strings and in case 1
in the middle. Is this normal? Which is correct?
Cheers
Anton