Perhaps Francisco is expecting the text not to be selected in the popover. (When it’s selected, of course typing anything replaces everything that was there before. The solution is to use the arrow keys to move to where you want to edit.)
Perhaps this expectation is set up by the way other things work …
I noticed yesterday the opposite problem when moving to change another value in Properties: When I hit Tab to move from, e.g., X to Y offset, I expect to type over the existing value. Instead, I see Dorico select and then deselect to the right the text in the field. This is unnecessary (because typing up & down arrows increments the field whether the text is selected or not) and very much the opposite of what I expect when tabbing to a field.
Example: Y = -1 and I want to make it -2 and I’m in the X field: I expect to type Tab-2. When I do that, I get -12 (because it ignores my typing - since it’s not at the beginning).
If I want to use the += type of math operations in the field, I can’t do it unless I delete and type over the existing value! So this deselecting is completely the opposite of the behavior I’m expecting for every reason.