that's this gravestone mod you're talking about http://www.minecraftforum.net/topic/1711328-164-smp-gravestone-mod-v244/If I recall correctly, grave stones in open blocks are disabled by default because of issues like these.
I highly recommend the GraveStone mod for its implementation. It is very configurable (to the point of saving all your items and placing gravestones in mid-air if there's no other option) and has some fun worldgen options.
I agree with this. After learning what happened to a friend when he had a knapsack and died, I never use them anymore. I use the Golden Bag of Holding for most of my on-the-go storage, and an Ender Pouch to send stuff back to my base.I don't even use the TiCo knapsack due to it losing inventory upon death. I've lost primo gear due to that so it's useless to me. I prefer an ender pouch with inception of backpacks or force packs
My experience is that this is either intended or just bad implementation by Tinker's Construct. Dartcraft's backpacks, for example, will keep their inventory on death. So will any force wrench'd tile entities. Both properly go into and come out of a grave stone from gravestonemod. When the config for ignoring terrain and placing gravestones exactly on the spot of death (regardless of water/lava/mid-air), the grave will be on the same point as the "Latest Death" waypoint from voxel/zan's minimap.this problem is hard to solve, as the 2 other gravestone mods have the same problem.
if you die near water, the spot where the gravestone wants to randomly spawn might be in a liquid, thus is cannot spawn
you might say then why not just spawn in water? well, what if you died in a lava lake... you'll need fire potions and alot of luck finding the grave back.
but what about normal water? that shouldn't be bad? but what if you died in an ocean biome and you're grave is like 20 blocks under water?
what the graves then usually do is search for another spot to spawn, but further away. this can end up spawning the grave in some very weird and far away spots.
I don't think there's really a fix for this, but what the gravestones could perhaps do is add a waypoint to a player's minimap for locating the grave easier