It is using the smart app driver, like CC.
Does the list of supported formats sent to calibre imply an order?. In that case I'm afraid that docx takes precendence over epub:
https://github.com/koreader/koreader...extensions.lua
There's no gui to change the list of supported files on KOReader, but OP can create its own set of supported extensions to send to the server.
Just create a file named calibre-extensions.lua in dataDir (that would be /sdcard/koreader on most android devices) with the desired extensions, like:
Code:
return {
"epub",
"fb2",
"pdf",
}
Save it and restart the client/program.