App crash on exit using Client Data Sets

[FrankThynne]

I'm experimenting with migrating from TSQL queries to TDatasetProvider and TClientDataset. The provider objects still look at TSQL queries. The data is in Paradox tables.

Thus, whereas I previously had

TSQL object (with TUpdateSQL object)
TDataSource

I now have

TSQL object (with TUpdateSQL object)
TDataSetProvider
TClientDataSet
TDataSource

The TUpdateSQL objects are needed because the queries involve joins, so I have to specify which table to update.

The TDataSetProviders and TClientDatasets have default options.

At last I have proper refreshing of queries with joins, but the application now sometimes crashes on exit after posting a change, applying updates and refreshing the dataset. The error isn't always the same (variously write to illegal address, error in unknown, error in kernel).

Any idea what I've forgotten to do?