For some reason, you've posted this to the Bug Report forum, which may reduce the number of responses you get.
I'd take a look at combining two features of filemaker to make one set of button provide all the fuctionality of all your button groups.
You can make a text field a button. Thus, you can change the name of a button by editing the field. It's often useful to make this field a global field.
You can use Button setup... to pass a parameter to a button's script. These parameter expressions can be set up as calculations to pass different values depending on how the expression evaluates. For example, your calculation can refer to your popup and use a case statment to pass a different value. Your script can then use the parameter to perform different operations depending on the parameter value.
"I'm not using a portal here because the info in the listbox/button group doesn't come from a table."
Are you sure you couldn't load the data into a related table anyway? It might be simpler.
You can also display multi-line data in a single text field and overlay the text field with a series of transparent buttons. The buttons can pass the line number as a parameter and your script can use that number to extract the correct line of text from the text field.