[firedrake] leaking memory

Dear all, I am experiencing a memory leak in our vertical slice model and wonder if there is any possibility of leaking memory associated with .assign(). Here I have a stand-alone code with the same function spaces and variable settings we use in the slice model: https://bitbucket.org/hyamazak/test_files/src/f455e7e68722c9264845a8426ba91c... What I do here is just doing new.vars += Deltavars old.vars.assign(new.vars) over and over again, and I see a constant increase of the memory usage both on my Linux and Macbook. I believe new.vars += Deltavars is not the source of leaking and wonder if there is any problem with doing old.vars.assign(new.vars). Do let me know if you have any ideas, all the best, Hiroe