A bit hard to say without seeing the stove design in question, but in chimney-style stoves, I've found that it's due to inadequate airflow through the burner, so the flame front moves back into the body of the burner. More, or larger intake holes may help.
One other common problem with chimney burners is too small a chimney opening, which causes 'flame lift-off', due to excessive chimney velocity, so the flame front rises above the hole, and often snuffs itself out.
For jetted burners with an open central fuel reservoir, too small an opening can prevent priming, as air cannot get into the reservoir to sustain the initial burn before the jets are established. Not a backfire problem, but a related issue.