Thanks for using Syncfusion products.
We have analyzed the reported issue (Checkbox always posts “Yes” to the value even if it is unchecked.) with our sample in the Version 220.127.116.11 and we are unable to reproduce the issue in our end. We have prepared the sample based on your requirement and the same can be downloaded from the following location.
In this sample the value “Yes” will get posted only if the check box has been checked. Kindly check with the sample and let us know if you would require any further assistance.
We were able to reproduce the problem (Checkbox value gets posted even if it is unchecked in unobtrusive enabled state) and we have logged a report regarding this. A support incident to track the status of this defect has been created under your account. Please log on to our support website to check for further updates.
Please let me know if you have any questions.