Plugins not enabled when added to history stack
When a plugin is added to the history stack (in dt_dev_add_history_item), they are not automatically marked as enabled. This has the effect in the GUI that the first adjustment of a setting in an inactive plugin does not affect the image, since the plugin will only be enabled on the second adjustment.
1. Open any image in darkroom mode.
2. Click on the "0 - original" line in the history panel.
3. Open the "exposure" plugin without enabling it.
4. Click once on either the left or right arrows of either the "black" or "exposure" sliders.
5. The top of the history stack is now "1 - exposure (off)" instead of "(on)"
6. Click again on anything in exposure and it will now be enabled.
This same problem can be exhibited with other plugins. I have tested with the "tonemapping", "overexposed", "velvia", "vignetting", "local contrast", "grain", and of course "exposure" plugins, so I would say it's a generic issue.
I am running darktable from current git sources.