Hi Adrian,
Thanks for your quick feedback!
In the jsfiddle example, I added a second copy of the table similar to the one in our app, and it appears to work correctly just by removing the separator.
In the actual application, where we have the freeze/unfreeze columns options first, followed by a separator, and then the filters, the problem would still occur after the separator was removed. It works correctly if there are no items at all before the filtering options. I was able to resolve it in the app by moving the separator below the filtering options, and then the frozen columns after that.
The problem, then, appears to not be specifically with the separator line, but more of a general issue with the menu ordering.
Thanks for your support!