Hi, We've been working with the planner for a while now, and every now and again we run into issues where the details captured on a task disappears on re-opening or the details captured on one task would appear randomly on other tasks. This happens randomly, or at least we have not been able to figure out what the sequence of events are that causes this.
We have similar experience for your first case (task disappears on re-opening). We use to do a force refresh (ctrl+F5) and add the description again which worked. But we have not faced the another issue (one task detail appear randomly on other tasks).