Kerbal Space Program

• Create a spacecraft in the VAB, and give it a name, say "x"
• Create another spacecraft in the SPH, and give it the same name "x"
• Return to the VAB, and load the SPH version of "x"
• Hit the save button

You've just lost your VAB version of "x" which might or might not have taken hours to create.

While the practice of creating a craft in the "other" facility is common, I still think it's prudent to give a warning in these cases that you're about to overwrite your "other" version of the craft with the same name in case a mistake is made. Proper UI design states that any action that can result in severe loss of work should either have an "undo" function or issue a warning before being executed; this is one of those cases.