What board are you using and can you confirm that this bug is still present in David's new 1.19 release?
You can update the web interface by uploading the DWC zip file on the Settings page too. Recent DWC versions automatically unpack and upload the compressed files.
Thanks for the hint, I had no idea you can upload zip-file. But at any rate, I did solve it originally by being persistent and I had a backup plan of taking out sd card, but I do think the bug may need attention. And yes, I can confirm it's still present in 1.19, except for I didn't have enough patience to finally upload over ftp this time and fell back to uploading .zip file (thanks again). Though I did have uploads of various size, language.xml.gz is 62126, I had 60448 and 59576 uploads instead. My board is according to DWC "Duet WiFi 1.0". The rest of components are all "1.19". If there's more detailed information about the board available somewhere, let me know where to find it. It's relatively early board, I don't remember exact days, but not experimental or something.
I also tried turning debugging on (M111 S1), I suspected maybe some error accessing sd card or some such, but nothing was obviously wrong on the wire.
Let me know if I can be of more help diagnosing it.