Gravity interaction error for large number of top level cells

Running a typical planetary impact simulation with a large number of top level cells (which runs faster) hits the following debug check before the 1st step: runner_others.c:runner_do_end_grav_force():688: g-particle (id=8954476, type=Gas) did not interact gravitationally with all other gparts gp->num_interacted=5017400, total_gparts=10285648 (local num_gparts=10285648 inhibited_gparts=0)

This happens for max_top_level_cells (max tlc) >= 99, no problem with tlc <= 98. (Note the .yml value isn't always what swift uses, so e.g. I could test tlc=101 but not 100.) This example has ~10^7 particles. I tried a variety of tlc values for the EarthImpact example with ~10^5 particles and another similar scenario with ~10^6, but neither hit the issue.

Latest master, ./configure --with-hydro=planetary --with-equation-of-state=planetary --with-gravity=basic --with-tbbmalloc --with-parmetis --enable-ipo --enable-debug --enable-debugging-checks, ../../swiftsim_test/examples/swift -G -s -a -t 12 -n 1 -v 1 pE_T20_Th_T20_B45v100_1e7__.yml

Input and output files: http://astro.dur.ac.uk/~cklv53/issue/