I think I identified a nasty bug in eZ Studio (which might have caused many weird behavior).

Follow the steps below:

prerequisite: I use the current install on sales cloud demo system where it is possible to try to post to the server files that are bigger than what the system allows. There was no file size limit in the content type, to test, you must make sure you don't have file size limit.

test scenario:

#1 post a simple blog post in Page mode, with no picture: success
#2 post a blog post in Page mode, with an image heavier than what is allowed by the system : error after publishing
#3 post a simple blog post in Page mode, with no picture : now error again (when it should be the same as step #1)
#4 try again #3, no change
#5 go in Content mode, try to post again a super simple blog post with no image: success!
#6 now I go back again in Page mode, try to post again a super simple blog post: success again.

I reproduced this sequence 3 times, so it's fairly solid.
It looks to me like if there are some edge case in the management of error handling, and that in Page mode a publishing error persist in the session when it should not, and that going in Content mode make it possible to purge the error.

See the attached video which follows the step above, to make it not too heavy I downgraded a lot the quality.