Open that snippet: DHTMLX Snippet Tool
and click on “Validate” button. Now, you can notice, that my css “any_class” was concatenated with validation class “dhx_form-group–state_error” without space, so none of them works properly.
But now error class is not applied at all. See that modified snippet: DHTMLX Snippet Tool and click “Validate” button there. Input is bordered with red color, but combo not. Previously error class was applied to combo also but with error, now it isn’t and there is difference about look between different controls.
It is still because of the original issue, the “any_class” is written into the class list of the combo list without space:
“any_classdhx_form-group–state_error”
Easy to check/validate when you add spaces to the class in form config
css: ’ any_class ',
Adding spaces here makes it work.
How lucky we are that leading and trailing spaces in the css form definition field are not stripped 
Yeah, I overlooked that my class is applied to two nodes, and there is one node with problem that I described in my first post:
My apologies.
You’re right. The problem was confirmed. We’ll try to fix it in one of the future updates.
For now I can suggest you to include the additional space in your class name as a workaround.
Thank you for your report.
We have fixed your reported problem in the latest dhx.Suite update (v8.1.1).
Now the appended classes should not mess.
Please, download the latest available dhx.Suite build to get this fix.
Thank you for your report.
Best regards.