Why doesn't the Quartus II software correctly synthesize signed packed array variables in SystemVerilog?

Due to a problem in the Quartus® II software, signed packed array variables in SystemVerilog may not be synthesized correctly. This problem may occur when assigning a one-dimensional array variable to a signed packed array variable if the index range is not explicitly specified.

For example, the following code may be synthesized incorrectly by the Quartus II software:

logic clk;
logic signed [3:0][31:0] packed_array_variable;
logic signed [31:0] array_variable;

always_ff @ (posedge clk)
    packed_array_variable[0] <= array_variable;

To work around this problem, explicitly declare the index range when assigning a one-dimensional array variable to a packed array variable.

For example, in the above code, change the last line to:

    packed_array_variable[0][31:0] <= array_variable;