gvim key mappings under alt results in special characters

For some reason gVim (debian stretch + kde) started to map Alt+i to "é" and Alt + other characters are also tied to some special letters e.g. Atl+o="ï" and Alt+p="ð". The problem is that this key mappings are nowhere set in gvim. Further, gVim is the application under KDE in which this happens (tried in Vim, Firefox, Kate, KWrite, terminal). So, while in some oses (Windows) this seems to be a standard mapping (however based on the current keyboard selection e.g. Atl+V = "@" in Czech keyboard but not US keyboard), I do not seem to see the same case in Debian+KDE. The question, where do these mappings come from? How to get rid of those so that the standard mappings in vim latex start to work again (Alt+I = new item in itemize).