Thanks for the client-side sort-by-column feature.
Basically, it does the job, but there are numerous problems with it. Rather than list them all, let me name just one, which when fixed, may eliminate some of the others.
Namely, the header row itself, 'Betrifft Kommentar Verfasser Start ...' etc should not be sorted. Currently, clicking 'Betrifft' will send the header row down between the 'A' topics and the 'C' topics, which is not what you want--you want the header row to remain at the top.
I notice also that you have embedded event triggers right in the table code. (Betrifft). Not only is this messy, it's unnecessary.
You can keep the Html completely pure, and have the events trigger properly by proper use of css and external js, leaving the Html completely clean and easier to create, read, and debug.
The "Unobtrusive DHTML" movement, if that's not too big a word for it, it a great way to accomplish this. See Stuart Langridge's pages on this topic.
For using unobtrusive DHTML to create click-sortable table columns see http://www.kryogenix.org/code/browser/sorttable/.
It's simple and clear, the Html table code is simple (it's nothing but a pure-Html table), the js is external and once working, will power all sortable tables simply by adding a class to any table, no in-line js needed.
Have a look, you won't be sorry.