In order to use a kendo combobox in an editable kendo grid, you have to bind it to an object with two properties (1 for the value and 1 for the text) - unless you happen to be in the fairly unusual scenario where the value and text are the same.

However, in a standard form, you can only bind a kendo combobox to a primitive type for the value.  There is no way to bind to an object, which is required in the context of a kendo grid. 

So what is required in the grid, is not supported in a standard form.  I don't understand the complexities of why that is, but this inconsistency does not make for a good developer experience.  It results in either creating different EditorTemplates for the two cases, or binding to the generic "object" - which introduces other challenges / issues.  Also - it means there is no good way to post the text back to the server when the kendo combobox is used in a standard form.

See here for more details:
https://www.telerik.com/account/support-tickets/view-ticket?threadid=609934