thinkr
EDIT: It turns out this whole problem was caused by a bug in wget.exe. It doesn't do uploads. I switched to curl and everything works fine.
Using wget.exe (version 1.18) I was trying to upload a file, going through all the various formats to see if it was something at my end. Abyss kept sending back 400 codes. Worked fine with file sizes below 8k.
Replacing wget with curl made everything work fine.