Software updates fix bugs and often add features, but they also come with the threat of breaking things that work or creating new problems. The recent Legacy update from v1.52 to 1.53 has introduced a potential problem for unwary users. The update added an "AUX3" icon to middle spot in the bottom row on the CAB-2 unit screen. This icon button is reserved for a future feature. Pressing it does nothing for the American Flyer Y-3, SD70ACe, or ES44AC, but it sends the Challenger immediately into full speed in the last selected direction. I accidentally hit the button and the Challenger took off at top speed, derailing five cars in a coal drag, and heading for disaster until I threw an emergency cut-off switch. (The U33C might also react the same way, but I don't have that locomotive. It, like the Challenger, is Legacy AC-power only).
The bugs that v1.53 fixed were not present in my Legacy system at v1.52, so I plan to revert to the older software to avoid any accidental launches of the Challenger that might cause real damage. I am posting this caution to anyone considering the update who has older Legacy locomotives.