It's hasn'thappened to me (yet), but I could certainly see why it could happen very easily. There is, however, a very easy way of getting round the problem. When an alteration is made on the legs page, the new route is shown on the map with a dashed white line. It really is a simple matter of checking the modification makes sense before executing the change.. .. .I realise it might sound holier-than-thou, but I make sure I do this every time and I know certain airlines insist on a cross-check before any changes are made.. .. .The AA 757 in Cali could have have made their lives alot easier (and longer) if they'd had a look at their map before pressing 'go'. I'm not slamming the guys, but I've learnt a lot from their mistakes.. .. .So if COSTA disappears off the map at 90 degrees and the legs page shows a few hundred miles away, then it is a safe bet you've done something wrong and it's either time to get out the chart or ask the friendly person on the ground.