Unable to fuse 1 Rune
It is not always possible to fuse 1 rune. When 4 for 1 is selected it snaps back to 2 for 8.
Below is a gif showing the issue. Note that it work for some amounts, but not all.
1. Suppression : 12 total, 12/3 max - fail to fuse 1
2. Ravage : 14 total, 12/3 max - fail to fuse 1
3. Heaven's Fury : 10 total, 8/2 max - OK
4. Revival : 31 total, 28/7 max - OK (Though slider snaps up one step)