This question already has an answer here:
When attempting to add a comment on the mobile version of stack overflow that is too long to be allowed simply nothing happens. This is in contrast to the main version of the site where the text below indicates "too long by 16 characters".
I have myself tried to add a (slightly too long) comment and had the "add comment" button appear to be broken; I then tried reloading the page and then closing the entire browser and reloading before I eventually realised that my comment was too long.
My feature request is therefore that a pop up dialogue (similar to the mobile comment deletion confirmation dialogue) appears where a comment is invalid due to excessive length.
In case its supposed to do this already and this is a bug not a feature request; I’m using the default browser on Android 4.1.2 (Jelly bean) on a Samsung galaxy s3.