Game Piece Inventory - expression evaluation

This may be a bug, feature request, or user error…

I am trying to build a inventory of pieces that shows summary level info (individual piece location is less important).

The properties I care about are 1) country 2) unit_type 3) unit_max_strength
I need to be able to show the SUM of how many of each unit type are on the MainMap.

I have been able to get something in the following format to work, using each property individually in “Sort & Group by Property”, which works as follows:
German (total = 3)
*Infantry (total = 3)
**4 (total = 2)
***unit1
***unit2
**3 (total = 1)
***unit3

What I would like to do is to concatenate the 2nd & 3rd properties to give a display like the following:
German (total =3)
*Infantry 4 (total = 2)
**unit1
**unit2
*Infantry 3 (total = 1)
**unit3

I tried to use a concatenated expression in “Sort & Group by Property” as the 2nd level
unit_type && unit_max_strength (I also tried w/ brackets {} and without spaces)

To concatenate two strings, you need to use “+”, not “&&”. So, {unit_type + " " + unit_max_strength} would be the correct syntax. If that field doesn’t support Beanshell expressions, then instead, you could add a Calculated Property to your units, with that formula as the expression, then use that new CP in the GPIW (Note that with CPs, the curly braces “{}” are assumed, and should not be typed).