BUG: header input filter doesnt get rendered when colspan is set

When i introduce colspan in the header with content “inputFilter” the input doesnt get rendered.
What is even more strange is that when i init the grid with custom css and modify the height of the header cell the input is displayed but with visual glitches.

And for got sake when i press F12 to check what is going on in the debug console… u guys really need to learn some html!!!

Example: DHTMLX Snippet Tool

custom css that makes the input display but causes visual glitches :

.form-grid .dhx_header-row .dhx_grid-header-cell:last-child {
    border-right: 0px;
}
.form-grid .dhx_header-row:first-child {
    height: 20px !important;
}
.form-grid .dhx_header-row:first-child .dhx_grid-header-cell {
    height: 20px !important;
}