As soon as you focus a textarea with the markdown editor (e.g. Talk submission > abstract or Profile > biography), the handle to resize it disappears. This is caused by the js adding an inline style, resize=none. As someone who likes to resize the textarea to be much larger than required, I think resize=vertical would be the best option here.

From a quick check of http://demo.osem.io/conferences/osemdemo/program/proposals/new, this seems to be an upstream issue (perhaps even in the markdown editor, if that's a separate library?). I'm happy to submit an issue either to https://github.com/openSUSE/osem or to another place (in which case I'll need pointing in the right direction).