I encountered this bug with NUI, where if you open a <select> dropdown and scroll up or down the dropdown will close again. I tested this without any css or javascript in the resource.
Bug video:
Code Used:
<html>
<body style="text-align: center">
<select>
<option value = "" selected disabled hidden>Dropdown</option>
<option value = "-1">Item</option>
<option value = "0">Item</option>
<option value = "1">Item</option>
<option value = "2">Item</option>
<option value = "3">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
<option value = "4">Item</option>
</select>
</body>
</html>