Lava tiled and froze a sandstone vein, mined it open and strong walled it shut, reopened it to find the sandstone vein returned, same ql and amount so I mined it out by hand, collapsed it shut and reopened next to it to find it is back again. This could also become an exploited bug if it was say a high ql silver/ gold vein that could be closed and reopened over and over again.