CKeditor: upload image plugin 'uploading status' incorrect
<p>Im using CKeditor version 4.5.8 in 'inline' mode (so directly in the content with the 'contenteditable' html attribute). This all works fine, except for one thing. I've added the '<a href="http://ckeditor.com/addon/uploadimage" rel="nofollow noreferrer">Image upload</a>' plugin, to add support for uploading an image while it's drag/dropped in the editor. This all works pretty good, except for one thing I can't get to work:
when dropping the image in the editor there should be a 'uploading' progressbar (tested in Chrome and in Firefox). But instead I almost directly see the message 'Upload complete'. But, at that time the upload is not completed (I've added a debugger breakpoint I my code to assure this is the case) and the 'success' response is not yet received (I see it as 'Pending' in the developer tools 'Network Tab'.).</p>

<p>However, when I 'throttle' the connection via Chrome dev tools, I do see a progressbar, however it's not showing the upload progress, but a 'Internal progress' of the browser of somekind? See screenshot:
<a href="https://i.stack.imgur.com/mCSNg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mCSNg.png" alt="chrome devtools"></a></p>

<p>Any ideas how to fix this?</p>