The last sign of the constant declaration is missing in the HTML documentation if there is at least on bracket pair ().

Source:
  constant MEM_ADDR_BITS_NAT_C : natural := 8;
  constant MEM_ADDR_MAX_SLOT_NAT_C : natural := 2**MEM_ADDR_BITS_NAT_C - 1;
  constant MEM_ADDR_MAX_SLOT2_NAT_C : natural := (2**MEM_ADDR_BITS_NAT_C) - 1;
  constant MEM_ADDR_MAX_SLOT3_NAT_C : natural := ((2**MEM_ADDR_BITS_NAT_C) - 1);

HTML output:
Constants
MEM_ADDR_BITS_NAT_C  	natural := 8
MEM_ADDR_MAX_SLOT_NAT_C  	natural := 2 ** MEM_ADDR_BITS_NAT_C - 1
MEM_ADDR_MAX_SLOT2_NAT_C  	natural := ( 2 ** MEM_ADDR_BITS_NAT_C ) -
MEM_ADDR_MAX_SLOT3_NAT_C  	natural := ( ( 2 ** MEM_ADDR_BITS_NAT_C ) - 1

As you can see there is a missing 1 in the third constant declaration output and a missing ) in the fourth constant declaration output. I've checked that the name length has no effect on the output. There must be a parsing problem with brackets there.
The first and the second output are correct because there are no brackets.