I think you are doing no wrong. It is just that those blogs you've been are experiencing some technical issues on their end that leads to comment attempts not accepted (or more precisely, giving you blank white page after clicking submit button). I am occasionally leaving comments on blogs with interesting topics that I can't get away from without leaving my thoughts on the comment section. That said, this scenario isn't new to me. Though it really frustrates me everytime it happens but what could I do? It is their blog not mine.
Additionally, I used to notepad my comments and save those URLs where I should put my comments on and get back at them after a few hours or a day or two. (I do this only if I really want to take part of the topic conversation.) If same scenario happens, I'd trash the file then.
Another thing you could do, if you really care, is to contact directly the blog owner and tell them what's happening on their blog. (You might end up not just putting your comment on their blog but having them on your partners page. Just an idea, I am not actually doing this part.)
There are plenty of blogs you could put your comments on. If one doesn't allow you because of whatever reasons, move to another. Time is gold. If you keep on thinking on this problem which is obviously not your fault might lower your productivity. So keep on moving.