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