Sounds like a version of the "Disco bug" already known in the Flyspray bugtracker (4400, 4415, 4745 - mostly obsolete screenshot links there as well, from years ago).
The reason is most probably that the address of a texture pointer got destroyed, it points now to a completely different texture than the desired landscape ground, and in your case, it was even a texture of a different application, used to display the text in your text editor. My first guess about what to blame for it would be your graphic driver...
I am almost sure that I have seen a screenshot with "text on landscape" before, but probably years ago, during v0.5.x.