Hi Anand,
Thank you for contacting Syncfusion support.
We have checked the reported behavior of DoubleTextBox by saving the input in to the DataTable in but we were unable to reproduce the mentioned behavior in our side. Value has been saved correctly in the DataTable which is used as the DataSource of another control. We have prepared a simple sample and video for your reference and it can be downloaded from the below location.
Can you check with the above video and sample for the scenario we have checked and let us know if we have misunderstood your query? Also, if possible can you modify the provided sample which replicates the issue?
Regards,
Keerthana J