I've ran into this as well with complex sounds.. especially if they have bass or wide range of frequencies, the algorhythm doesn't know what to do. But other slicing algorhythms I've tried react pretty similar. Ableton would probably do this too and has worse transient detection sometimes.. where they're all early or late. What helps sometimes is to place a DC filter or even a simple high-pass, low-pass. Synths can generate some extreme lows and highs that throw off the detection. When I record my synth I usually do that through a channelstrip VST to just clean up the sound going in. That makes slicing easier as well.