Hello @Rachquiat
I think I have replicated your issue. Tell me if this accurately describes your situation:
You have a mesh with an active deformer applied in move mode, but then you sculpt further on it in Draw mode. Upon re-entering Move mode and adjusting the deformer, any sculpting you did since enabling the deformer disappears.
This seems to apply to any active deformer, not just Bend Arc. I cannot say whether it is a bug, or simply a limitation of the tools. You should remove or Accept the current deformer before attempting any further sculpting.
If it IS a bug, to get technical attention for it you would need to report the issue to Pixologic Support.
Good luck! 