SSRS drop down selection blank after being repopulated

I have a SQL server 2005 report which has several drop downs that get populated by a stored proc based on the selection of another drop down. When a user changes the selection of the drop down that drives the population of the other drop downs, they get populated with the correct values, but the selection will be blank, rather than the default. If another selection is made, the drop downs that were blank from last time but didn't get repopulated this time will now have the default selection made.

This problem does not h开发者_JS百科appen when viewing the report in preview mode, only when rendered in an asp.net application. In the IsPostBack block there is nothing being done to the report at all, so I have no idea what could be causing this behaviour.

OK, I found the cause.

I'm not sure if this is isolated to 2005 but if the 'default values' array contains a value that doesn't appear in the current set of 'available values' then you get no default value selection. I can't quite explain the strange behaviour with this -- just make sure that you never insert a default value if it is not a subset of the results for the 'available values'.

Another excellent Microsoft "feature".