error message gets downloaded instead of rendered by Konqueror

[zooko]

I chose a file to upload, left the radiobutton set to Immutable, and clicked the "Upload" button. Konqueror then prompted me to save a file or open the file with a helper app. I chose to save the file. The contents of the resulting saved file were:

upload requires a name

There was no trailing newline.

This is with Konqueror 4.8.3.

Grepping the Tahoe source shows that this line is producing that error message.