[Bug TC6.01] appendtabs when tab header is hidden

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1) Disable the option "Show tabheader also when there is only one tab" in Configuration/Folder Tabs
2) close all tabs so the tab header is gone
3) append some tabs from a file with the appendtabs command via a button or otherwise
4) all new tabs should be appended at the end, but the first of the new tabs is placed before the original tab (the tab which had it's tab header hidden)