This is from Henning's website:
We only recommend using the shock buffers as a way to reduce impact stress on the practice range. For carry and competition, any consumable such as a shock buffer may be unreliable. Due to the size of the shock buffer and the reduced rear travel (0.080") caused by the shock buffer, the slide may or may not lock back on empty. There are modifications that can be done to the slide stop etc to ensure rear locking, but as mentioned, we recommend shock buffers as a training tool only.
It states there that the slide may not stay locked back.