Splitting a stack in Extended now throws a Lua error :
...ace\AddOns\totalRP3_Extended\inventory\container.lua:541: attempt to call upvalue 'OpenStackSplitFrame' (a nil value)
After looking at the UI code, there was a change with the function aforementioned, as illustrated by the use in ContainerFrame :

• 8.0 : https://github.com/Ellypse/wow-ui-source/blob/live/FrameXML/ContainerFrame.lua#L1316
• 8.1 : https://github.com/Ellypse/wow-ui-source/blob/ptr/FrameXML/ContainerFrame.lua#L1331

I will try to find a fix for this issue tomorrow afternoon, hopefully sneaking it in the 1.3 release.