I'm too suffering from almost random captcha requests...
It seems that
1. when provided images to key in text you don't loose the work
2. I'm not a robot tick box does loose work returning to the post, but blank!
I've not had enough to be 1000% sure, but that appears to be the end result, so maybe this is a simple fix between the 2 styles of captcha?
I've not tried saving drafts for a long while, so can't comment on that issue.
I'm accessing via various 4G dongles or WiFi hotspots from phones, but can post fine, then while on the same connection be later asked for catcha (so same IP, same session etc). So the triggering of the captcha still seems random!
On the subject of pictures, it would be really good if the 'hover tip' stated the 800px width restriction, that can't be too hard to achieve?
better still if you automatically uploaded and resized the images directly (some people will get lost hosting their own pcitures - maybe a link to a tutorial in the 'tip'?) ... and there are BBphp tools to do this, even to host the image on a separate sever to reduce your storage and bandwidth:http://postimage.org/mod.php
So no excuses!