File -> Import -> Plain text (join lines) opens new file

[Rich Shepard]

I've not before had this problem: importing a .txt file into a .lyx
document. I'm trying to import a file import.txt ($ file input.txt 
input.txt: UTF-8 Unicode text) into an open LyX document. Instead it opens a
new file called input.lyx.

What might I be doing incorrectly and not seeing?

TIA,

Rich