Thanks for reporting the issue!
Can you give more details on how to reproduce it?
I cannot seem to replicate it on my end for some reason.
And just to be sure: You are using the most recent version of the plugin, are you not?
Yes, I am using 1.16.3 and had just recently updated it.
Works even with an empty scene collection.
1. Add a macro
2. Select that macro and add two actions (in the lower box).
3. Change the type of the second one to "Audio" (just to make it distinct from the first action).
4. Hover over the second action to bring up the buttons specific to it. Click the delete button.
5. Action 2 (the "Audio" type) will remain, even if it is the one you deleted.
Second case:
1. Add two actions.
2. Change first one to "Audio".
3. Change second one to "Macro".
4. Delete second one.
5. The second one will remain.
Third case (no bug):
1. Add two actions.
2. Change first one to "Audio" (leave second one alone).
3. Delete second one.
4. The first one remains.
Upon further testing, it seems that it happens when you try to delete the last action, as it happened when I tried with three actions and deleted the last one. It deleted the first one instead.
On even further testing, it becomes unpredictable when you start changing action properties. Sometimes, there's no bug, sometimes there is.
Fourth case with bug:
1. Add three actions (they should all be "Switch Scene" type).
2. Change first one to Cut (leave the other properties alone).
3. Change second to Fade.
4. Change third to audio type.
5. Delete third. The first one will be deleted.
Some tests I did make me think that the bug is happening when you change the Macro action type. Perhaps the action order does not get updated properly when the action type is changed.
Fifth case with bug (this time, I'm deleting the middle one):
1. Add three actions.
2. Change them to "Current transition", "Cut", and "Fade" respectively (to distinguish them).
3. Change SECOND one to Audio type.
4. Delete second one. The first one will be deleted instead.
This happens even with four actions. just change either of the middle ones and delete it.