When going through the portal, the very 1st time i ended up dying with my grave being spawned over 100 blocks from my inital death point and each subsequent time i enterd the portal to goto the mist dimension id Enter with full health an hit an invisible wall or something an lose 3/4 of my health once it loaded the dimension or id end on half a heart having taken damage.

This is using All The Magic mod pack by All The Mods Team and is consistently reproducable on my end using vers c_08+ of the mod with Forge vers *.5.2807

This is strange, because the error with damage has long been fixed. Perhaps this is the influence of modpack.
As for the grave, the portal is very much open at coordinates different from the coordinates where it was built.

I havent had time as yet to test this in a world with just this mod present to see if it still occurs though.