VCS -xprop modes don't change == on replicated x; they move the mux

Tested VCS R-2020.12 and W-2024.09 with -xprop=tmerge/xmerge/vmerge, -O0, -Xnoopt and +rad on {4{en}} == const with en = x. No flag changes the comparison itself: impossible patterns (4'b0101) stay 0, reachable ones (4'b1111) stay x, and != stays x. -xprop only changes how the result flows through control: a ternary on the impossible compare goes from xx (default) to the false branch under any xprop mode. -O0/-Xnoopt change nothing; +rad makes only the uninitialized-variable form return x, not the = 1'bx form. So you can't flag your way to LRM-conformant == here, but no flag produced a wrong value on a reachable pattern either.