Plugin output in content pages always on top

Hey all,

to get to know monstra, i coded a small plugin just du check functionalities. Now I have the problem, that the output my plugin produces is always on top of the content section of pages, when i put the plugin shortcode into content pages, and not on its proper position where i put it in the content page. e.g:

content page:

<h1>My heading</h1>
{myplugin return="some string"}

will result in:

So the order changed and my plugin output is on top of the heading. Can't figure out the reason... can sb help me?

_Andreas

PS: from what I saw yet: monstra is awesome!