Saving the game issues

Upon turning lava into obsidian, I saved and quit standing on top of the obsidian. When I logged in the next day, the obsidian did not retain its state, but rather switched back to lava as though I had never turned it to obsidian, causing the death of my character, and loss of valuable diamonds. Most recent account, is I acquired a horse, traveled to my house and stationed him with a lead. Logged off, returned the next day, no horse or remnants.