Synopsis of runs which did not exhibit the instability discussed in Sect. 5. Crosses/black: a significant α²Ω mode was never developed (cf. Fig. 4), symbol size indicates the corresponding number of runs (1, 2 or 3). Square/blue: a transition occurred, size represents the time until transition (4 to 25t_res). Diamond/red: the α²Ω stage was entered, but no transition occurred. Size represents the time span of simulation (5 to 35t_res). Runs at the same position differ only in random seeds. Upper panel: high-shear runs, see Table 3 for those exhibiting a random transition. Lower panel: low-shear runs. Symbols scaled down by a factor of 3 with respect to upper panel. All runs in the lower panel had f₀ = 0.04.