Memory leak in Multilineeditbox

The map options window is almost unuseable. If I enter a few lines of text, the input becomes really slow (about 30 seconds per character), and eventually widelands doesn´t respond at all and I have to force-close it. The system monitor shows that widelands suddenly consumes all available RAM (2 GB) and the entire swap memory (before opening the map options it used ~20 MiB and no swap). The space isn´t freed when I close the map options dialogue, only when I exit widelands. I found this bug in current trunk (both debug and release) but not in build19.

https://wl.widelands.org/forum/topic/2786/?page=12#post-20126