Roy first reported this and Tony confirmed today that sometimes when you are using arrow up and arrow down on the keyboard to go thru records, that the customer code can accidentally change.
If/when you need to scroll thru records, you might want to move the cursor to another field. A non-drop down field like CSC.
The latest form fixes this problem by changing the first field on the M and V screens--be sure to ask for it from me. For the M screen the first field is the AAR600 box, instead of customer. The idea is that when you switch to that screen, AAR600 will "have focus", it will have the cursor, so if you then use arrow keys, customer won't be affected. The same goes for "surveyor name" field on the V screen. This will add an extra tab stop to your routine, but you'll adjust pretty easily. It is surely better than accidentally changing customer info.
Note, the switching values problem will (likely) still occur if your cursor is on another drop down, (e.g., location). My proposed fix is to reduce the chances of customer and valve mfg from changing when all you really want to do is cycle thru records.
Of course, if I find a better solution, I'll let you know. And you, should do the same.