Sounds like a momentary lean condition. The transient fuel demand when flooring it after a gear change can be pretty huge.
Either that or something is amiss and the ECU is pulling back. Over boosting maybe? Anything revealing in the logs? As always, best to use VCDS in turbo mode.
Did some logs a while ago before the refurbed injectors went in (and the misfire was really bad) and the car behaved itself so left us clueless.
Since fitting the injectors it's like a different car... apart from this very rare but specific hiccup which manifested after the injectors went in.
I don't have VCDS, and even if I did I'd be waiting weeks or months for it to happen again. It seldom happens. I don't know if the fact I'm still on a Stage 2 map but with a Loba pump has any bearing on it, but logic tells me that if anything I should have more fuel headroom than if I was on 2+, so I doubt that.
I know I'm just guessing without doing more logging though. Although if it was momentarily overboosting like you suggest then it might have stored a code.