I am using OpenLP 2.1.6 on Windows 10.
We have just upgraded.
The first time I edited a custom slide, I ended up with a new slide.
The second time I edited a custom slide, I ended up with a new slide.<br>
The third time I edited a custom slide, I ended up with only one slide as expected.<br>
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I now have two new slides and two old slides. One pair has the same title, the other pair I changed the title.
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This seems to be a bug, and I will keep my eyes open to see how things go. OpenLP is working fine and stable.