Meaning to store images to "img" directory on disk I defined 'QA_BLOBS_DIRECTORY' as it written in config file instruction.
After that images are being saved both on disk and in 'qa_blobs' table in MySQL db. Thus storing blobs to database is continuing.
Moreover in post images are loaded from database instead of "images" directory of the site.
Standard WYSIWYG editor is used, but it's unlikely the source of the bug.
I had checked "images" dir and found that all pics are uploaded successfully and accessable in internet browser.