A negative return on a cash holding can be due to performance being calculated inclusive of fees and taxes.
Potential solutions are:
1 Run the IPS Performance report before fees and taxes which provides a more logical return.
2. Exclude the cash accounts from your performance report from under the client's Portfolio (see below). Note: If you can't see the option to Toggle Exclude from Reports then please select 'No aggregate' under Aggregation: in the filter options.