Error when switch windows back to :Tree buffer

if I split windows, and then trick to <C+w>h back left to the TreeBuffer view, I get the following error at the bottom of vim
```
Error detected while processing WinEnter Autocommands for "BufferTree"..function RefreshBuffer:
line    3:
E475: Invalid argument: -1
```

However it does seem to go back to the buffer fine. vim 8.2 on mac.