I found on TTMSFMXCustomGrid :
if an exception occurs while HideEdit is executing, EditControl is not Hide which is normal but then it's possible to edit other cells and EditControls are never Hidden.
This behaviour is due to FBlockEdit which is not set to False if an exception is raised, because HideEdit is not executed if FBlockEdit is set to True.
To fix this I surround the code following "FBlockHide := True;" with a Try/Finally and set FBlockEdit to False in the finally.
Can you perhaps provide us with a sample that demonstrates the exception?
Just place a grid binded to a DataGeneratorAdatapter on a grid an raise an exception in an event triggered during HideHedit such as OnCellEditValidateData.
It's more visible with custom editors like comboBox or DateTimePicker.
We will investigate here if we can improve this behavior.