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selected text in dhtmlxCombo

after selecting any option from drop down nothing will appear in options again until and unless I remove the selected one.
My requirement is, if I select something from options then that should be selected and all other options should come in drop down.

is it possible?

The described behavior is correct one, if you are using filtering mode. 
Please check 
           http://dhtmlx.com/docs/products/kb/index.shtml?cat=recent&q=6207
you can use same approach, but use onChange event instead of onOpen