Did you try to load a large amount of record in the WebCombo? If that is the case, you could try using load on demand in WebCombo to improve the performance.

A sample has been provided in WebCombo sample on the page LoadOnDemand.aspx

I am very sorry for the late reply. I have increased this issue bug report priority, however I still do not have a fixed date when the fix will be available.

A sample of client binding and batch update has been provided on the ClientBinding_BatchUpdate.aspx sample page.

You will need to set the BatchUpdateMethod property in the ServiceMethods of ClientBindingSettings. Here is an excerpt of the ClientBindingSettings from the sample:

<ClientBindingSettings DataLoadMode="PagedData" DataSourceType="WebService" ItemTypeName="Bug"
    ServiceUrl="WebService.asmx">
    <ServiceMethods BatchUpdateMethod="UpdateBugs" SelectMethod="GetPagedBugs" />
</ClientBindingSettings>

Currently UXTextBox has not supported masked input. Masked input is being considered as a ClientUI control for the next ClientUI version.

A more detailed ClientUI documentation is being prepared, this documentation also include the whitepaper with properties and method list, and will be released soon.

Have you trind manually updating the database instead of using WebGridDataProvider? After a successful operation, you will need to return TransactionResult object as detaild in the article "Transaction Operations (Insert, Update and Delete)" in the WebGrid documentation. 

Here is the update snippet for a composite table, exception handling is not implemented: 

[WebMethod]
[GenerateScriptType(typeof(BugCustom))]
public TransactionResult UpdateBugsCustom(List<ClientRowChanges> changes)
{
    BugTrackerEntities context = new BugTrackerEntities();

    BugTrackerModel.Bug bSingle = null;
    BugTrackerModel.Owner oSingle = null;

    foreach(ClientRowChanges change in changes)
    {
        BugCustom currRow = (BugCustom)change.NewObject;
        bSingle = context.Bugs.SingleOrDefault(b => b.BugId == currRow.BugId);
        bSingle.Summary = currRow.Summary;

        oSingle = context.Owners.SingleOrDefault(o => o.OwnerID == currRow.OwnerID);
        oSingle.OwnerName = currRow.OwnerName;
    }
        
    int saveResult = context.SaveChanges();

    return new TransactionResult(){
        AffectedResults = saveResult,
        OperationType = DataSourceOperation.BatchUpdate,
        ReturnValue = true  
    };
}