It happened to me twice. I don't know what the cause is.
Terminology is splitted in two. I was compiling and waiting on one. When I needed to put my sudo password, I noted it wrote it in both splits. Every keyboard event is sent to both splits. If I run a command, it executes it on both. I couldn't split more with the shortcuts so I tried to split with the menu. That worked but then, every time I pressed enter, it was splitting more.
Logically, Ctrl-D closed all the splits together.
Is it a bug or a feature? :-)