Hey Ben. I did just a quick test with Coffee Chain and Superstore extracts in my 10.0 environment and things work as expected. I published my simple workbook on public if you want to try it on your server or let me know what you're doing differently.
Curiously, the query parm for Region doesn't seem to be working on Online, though.
I am also having an issue when using URL filters with multiple TDE's connected with cross data source filters. Using URL filters I am able to filter on only the dashboard from which the cross database filter is originating.
Here is the set up.
I have 4 data sources all with a common Org Unit. The Org unit while being present in all data sources, the filtering is originating from one data source and then applied to all related data sources (indicated by a database symbol with an orange checkbox). Filtering and drop-down functionality is working 100% however i am only able to set the value using a URL parameter on the dashboard where the filter is "sourced" from.
Im suspecting that either
A: You can only use URL filters on the dashboard with the originating cross datasource filter
B: The sets of data for the filtered field must be 100% matching (meaning contains the exact same distinct count of values)
C: Im doing Cross Data Base Filters wrong.
D: Something entirely different
Any help to me or the OP would be greatly appreciated