Slice Adjustment Strangness

I’m just editing a switch(value) it has 8 slices on each of 2 inputs, as I edit the slices in the inspector, after the 3rd slice as I edit the value and hit return I get an addtional slice added to the input, this has happened before recently but I put it down to having had the patch open for a long time, but this is a freshly opened patch (although it is a big one)
Anyone seen this?