thrila, I'm not sure if you use combat trims or manual trims, but the phenomenon you experienced effects all planes in AH - the deadly inverted flat spin..
!
When you go vertical up to too low a speed, then there's always a chance the reversal process gets screwed, and the plane starts to pivot on its yaw axis more than its pict axis.
The results are catastrohpic - the plane begins to fall down and lose altitude on backside. Some planes have a better chance to recover from this(like the Spitfires and 109s), but others(like the Ta152 or the P-51D) are very very hard to recover from it. Most often they auger straight down.
Now, I came to realize that the use of manual trim(especially elevator pitch in the neutral center position) lowers the chance of falling into a flat spin. Since combat trim does not react to the status of the plane, but rather is just a preset figure of trim values according to the plane's speed, when your plane goes vertical into extremely low speeds the elevator automatically trims almost full up. I think that results in a state equivalent of pulling the stick too hard at too low speeds - thus, during the vertical, with the elevator trim way up, the plane cannot reverse nose down in a natural manner and it falls into a spin.
However, when on manual trim, with the elevator trim centered, in most cases you can just ease on the stick and the plane flips over with ease.
To the Spit14, it might be especially dangerous in the verticals due to its massive torque.
