Generally, what would cause the cursor to stay locked in a combobox? Returning .F. or .T. from event code? Could it be problems with the ControlSource and/or RowSource not being in sync?

In the case of a control I am working with (codebook style incremental search), tabbing or pressing enter executes the code in the lostfocus event, but the cursor always returns back to the combobox rather than moving to the next control. This has been hard to troubleshoot because the control behaves correctly when I execute the lostfocus event code from the trace window!