Aggregate in Correlated SubQuery

Before postgresql 8.1.5, I could do the following to find the first
lead that created a prospect in my application.

SELECT
Lead.LeadID,
Prospect.ProspectID
FROM
Prospect INNER JOIN Lead USING (ProspectID)
WHERE
Lead.CreationDate = (SELECT MIN(Lead.CreationDate) FROM Lead AS LL
WHERE LL.ProspectID = Lead.ProspectID)

With 8.1.5 this now generates:
ERROR: aggregates not allowed in WHERE clause
SQL state: 42803

Shouldn't aggregate functions still work within correlated subQueries?
I saw in the 8.1.5 release notes that this was disabled due to crashes
this caused in 8.1.X versions for Postgresql. I have never experienced
this with queries similar to the above.