Vim syntax highlighting fails with autosession

Since I've installed this VIM autosession manager (which does its job) syntax highlighting gets killed on the first buffer change after starting vim. I can restore it with

:syntax on

but I would prefer not to have to. Maybe there is something in ~/.vim/after I could set?

Side question: I use VIM bundle; is it still ~/.vim/after ?

(I don't know if this matters: All I ever need syntax highlighting for are tex and lilypond files)

thanks

edit: here's a selection from my .vimrc - possibly a lot of stuff is redundant in there.

syntax enable

call pathogen#infect()

nmap <Tab> :bnext<CR>

filetype plugin on

filetype indent on

let g:tex_flavor="latex"

autocmd BufEnter Makefile* :set filetype=make

autocmd BufWinEnter . loadview

filetype off

set runtimepath+=/usr/share/lilypond/2.16.2/vim/

filetype on

syntax on

filetype plugin on