I could be wrong, but my understanding from someone else's explanation is that dyed leather is a special case added by Minecraft itself and bypasses the standard model system. Unfortunately, Forge doesn't allow this (well, it does, but it would mean I'd have to use the IItemRenderer like I do in 1.7 in 1.8, but it is now deprecated in 1.8).
The crash is caused by an issue with the code utilized to decode the hexadecimal string stored in the Item's NBT data. This is a relatively easy fix but I do not have the ability to post the update as this topic is under thisguys' control.
In case anyone else cared about the update, I don't know if or when it will be updated as I currently work ~65 hours a week plus any other obligations I have so I have very little time to learn the new system as well as update the mod. If I can I can, if I can't, thisguy will have to see if he can find yet another person to update BladeCraft.