Combobox : strange icon when unzooming

[fbockelee_echeneis]

with the standard snippet
https://snippet.dhtmlx.com/hj51as02

when unzooming with mouse (Ctrl & wheel down 2 times or more)
i have a strange icon wich appear just after the down icon on the right

any idea to avoid this strange icon ? note that this may also appear on grid filters

[cstff]

They look like unwanted buttons on a scroll bar

.dhx_combobox-input-list {
    overflow-y: hidden;
}