There are currently a couple of odd behaviour issues with the Onion Skin settings.
Firstly, the Onion Skin On/Off switching seems a bit erratic. The state of the onion skin on screen is not always reflected by the state of the on off switch - which can be confusing, and often means you have to open the editor and toggle both on off switches to get the desired result.
Secondly, the opacity sliders for Frames Before are not quite right. When there is only one before frame selected, the Start Opacity slider has no effect (it works in the preview image, but not on the stage). You have to adjust the End Opacity slider to change the opacity. Seems like a small issue, but onion skin selection and adjustment is something I do a lot, and this anomaly is constantly tripping me up! :-)
Customer support service by UserEcho