setting values on Levels adjustment layer via action/scripting doesn't work on grayscale documents

Hello,
The title said it all.
Steps to reproduce:
1. make a document with Grayscale color mode (or convert it via Image>Mode>Grayscale)
2. Add a Levels adjustment layer.​​​​​​​
3. record an action of you changing the sliders on the Levels adjustment layer.
4. change those values first, then try playing the action.
5. Result: it does nothing! (but such an action works on an RGB Document for example).

Besides that, RGB documents, for instance, allow the creation of a Levels adjustment layer with given values in a single executeaction step. that doesn’t work on Grayscale documents.