Thank you so much for looking at it! Sorry I missed your initial reply
I was not getting notification emails.
Looks like it's still happening in 3.8.60 if there is already a number in the field that has a decimal point. Here is how I was able to reproduce it:
Create new project.
Go immediately to the export settings dialog.
Go to "Pack Settings"
Type in 5.0 in the first scale box
Select the "5.0" and attempt to type ".5" to replace it. It will not accept the "." when you type it.