GROUP between rotated slits does not work

[willend]

(Initial bug report from @g5t)

In the attached example, two slits rotated in opposite directions are placed in a GROUP. As long as Ang=0 (i.e. the slits are not rotated), the GROUP works as expected.

Once a finite rotation is added, the second slit is no longer functional

Adding an ALLOW_BACKPROP; in the TRACE of Slit.comp brings the expected functionality (output from an Ang=10 run):

What this all-together means is that the RESTORE_NEUTRON associated with being !SCATTERED in a group element is not working. Code-generator massage needed. GROUP.instr.txt