I don't use that method to post pictures... here's what I do:
- Don't use the "Quick Reply" box
- Click the "Reply" button at the top right corner of the post you're replying to
- There's now an "Insert Image" button (with a tree on it) in the toolbar at the top of the Message box.
- Click the button and it opens an "image properties" screen
-Click "Choose File" to open a browserto allow you to select on your device to the image you want to upload.
- Make sure the image is not too large - max size 2.0MB
- Select the image, then click Upload. (Ignore the Server Error pop-up that might appear at this stage)
- Press OK. It will upload, just like these screenshots!