SSRS 2008 Sending Multi-Value Parameter to Another Report only send a few of the values

Scenario:

• I have a matrix with column values of EventDate, which is grouped by EventWeek
• I have EventType in my row value.
• I've successfully created links from the matrix to a drill through report for EventType and EventDate.
• However, this link doesn't work when i try to click on the EventType and EventWeek.
• I only receive a subset of the entire value (in fact I only get one day's worth of events).

Question: How do i get grouped value to work just like the details value?

Thanks in Advance.

KBC