In DSP48 Macro, the number of output ports depends on the device selected. There are two output ports with Virtex-6 devices and one output port for Virtex-4 devices for the same configuration.
When I change the device from Virtex-6 to Virtex-4 and the compilation is run, one output port disappears dynamically. This appears to be causing the block mask to disappear.
If after configuring the DSP48macro v2.1 you change the family to either Virtex-4 or Spartan-3/-3A/-3E in the System Generator token, it is recommended to reconfigure the DSP48 Macro 2.1 before compiling the design.
As with these families, additional ports (i.e., ACOUT, CARRYOUT and CARRYCASCOUT) are not supported.