Just thought of something, actually.
Part of the reason the full theme may be harder to post with on mobile could be the portal (left panel) functions. Those are mainly disabled in the current mobile theme. Only the shoutbox is called, and it's not called on the pages you post from (only visible on board index). Since the shoutbox reloads completely with every page load (ie: no caching) that is a fair bit extra to deal with. Ditto for recent posts.
This means that with them disabled there is less code to parse and fewer queries sent to the database, as well as less stuff sent back from the db. Now what this means is that, although enabling all the side panel functions is a cool idea, there is a chance that it will result in similar problems to what you had earlier. I'll be interested to see if this is the case.
To make the comparison easier I'll load the latest version as a separate theme rather than just overwriting the older files on our server. It may turn out to be necessary to disable some panel blocks on the mobile theme. I wont know until people try it and see how it goes. If disabling some of them is necessary it's possible to do that. Bit of a nuisance in terms of coding, but possible nonetheless.
I'm not sure if what you're suggesting is the cause of the posting problem after all. I've learnt, since writing the initial post where I reported the problem, that posting is much more consistent and reliable if i press the ' back' button on my android, after typing and before clicking on 'post'. This back button closes down the keyboard, therefore it seems that posting refused to work properly whenever the keyboard was showing on my android.
The bigger problem of not being able to see your reply properly when posting, because scrolling was temperamental and text was small, has already been solved in your new version. Therefore, I'd concentrate on other improvements rather than wasting your precious time on the posting issue?