DHTMLX Grid Fixed Headers

When setting a grid column with fixed cols and header it will set a high z-index which will overlap when adding floatable windows or other content in the DOM object.

Temporarily fixed by doing the following.

.dhx_header-fixed-cols {
z-index: 100 !important;

This issue did not exist prior to latest release 6.5.8

As of the latest release the z-index is set to 999999.

I apologize for the delay.
Could you please, provide a complete demo or a demo link, where the issue could be reconstructed locally.