I went looking online after writing the post, and it's a known issue. The firmware update is supposed to fix it, but there have been varying results, as you can see in this thread.

I hadn't noticed one way or another with the SD card, but I may not have been reading anything where the file's held on the card anyway, as it appears I still haven't got the knack of loading legible html files. :-/ I need to sit down and play with it properly regarding file transfer.