Didn't get to post in the 1. 4 thread.
The 'Load Previous' and 'Second Stage' dropdown boxes in the Missile Design page are linked, meaning when you try to select a missile to use as a second stage it loads the values of that missile, overwriting everything else.
Reproduced but haven't figured it out yet 
This bug is second only to Compressed fuel storage in annoyance value. I removed the code behind it and even deleted the box and replaced with a brand new one with a new name. Same problem
I'll come back to this later.
Going to have to do some speculation here, but this may help.
Assumption:You are passing the same list / array object to both dropdowns. Or are setting both lists from the same source (Ex:
var a = SomeQueryResultFromDb.ToList(); var b = SomeQueryResultFromDb.ToList();
)
This results in both lists effectively being the same thing (i. e. pointers to same memory location of actual primitives. )
The dropdown UI elements set some variable in the list of objects to true to indicate which one is selected. Since both (inadvertently) point to the same list, they both share the same 'select'.
Solution (If assumptions are true):Do a deep copy of the list before assigning it to the second dropdown.
var a = SomeQueryResultFromDb.ToList(); var b = SomeQueryResultFromDb.Select(existingDesign => new MissileDesign(existingDesign.Id, existingDesign.Name)).ToList();
Unrelated minor (non-fatal) UI bugs:In the Ground Forces window, in the Unit Class Design tab, if you click the first entry (The headers) of the list, you get error #2608 and #1838 "Object reference not set to instance of object. " in both cases.
Note: This is from the 1. 3 version, but I haven't seen anyone else mention it. (Also very minor, so only really reporting it for keeping track. )