Repro steps:
1. Create a new particle system.
2. Switch Start Size or Start Rotation from constant to curve.
3. In the curves preview, drag the curve and notice that there's 2 more curves under it.

Expected outcome: to just see 1 red curve.

Notes:
- happens across 5.5 and also in 5.6
- Works in 5.4.2p2
- workaround is toggling 3D size/rotation
- purely cosmetic: even though other curves can be manipulated, the system has 3D size/rotation turned off so it'll have no effect.