Health Regeneration NOT working after re-logging

When you apply yourself Regeneration level 255 (max you can in mc java) and stand in lava, the lava won't kill you; UNLESS you re-log. Once you re-log, standing in lava with regeneration 255, the lava won't hurt you for the first few seconds, then start killing you even though it shouldn't be able to. (I can't fit the video because the video size limits to 10MB, max I can compress it to is 12MB)