Sybase database sizes procedure, mostly working but found a weird result

I asked for help with my Sybase procedure with returns database sizes at question: https://www.experts-exchange.com/Database/Sybase/Q_27421159.html?cid=1575

The newly written procedure works greats but I hastily closed the question before I noticed a problem with the result.

 Type  Used                        Allotted                    PercentFull
 ----- --------------------------- --------------------------- ---------------------------
 data                   202.000000                  300.000000                   67.333333
 log                      1.000000                  350.000000                    0.285714
 total                  202.000000                  650.000000                   31.076923

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Total used should be 203 here.

Any idea why this is happening?

use sybsystemprocs
go

if exists (select 1 from sysobjects where type = "P" and name="sp_dbacapacity2")
   drop proc sp_dbacapacity2
go

create 	proc sp_dbacapacity2
	@dbname varchar(30)='null'
,	@type varchar(30)='null'
as

declare @Mb int

select	@Mb=1024*1024
-- number of pages * @@maxpagesize / @Mb gives us size in Mb
-- NOTE: we must use @@maxpagesize, not @@pagesize which is always 2049 regardless of actual page size

select	Type =	convert(varchar(5), "data")
,	Unused = convert(numeric(15,6),	isnull(sum(curunreservedpgs(u.dbid, u.lstart, u.unreservedpgs)),0)*@@maxpagesize/@Mb)
,	Allotted = convert(numeric(15,6), isnull(1.0*sum(u.size)*@@maxpagesize/@Mb, 1))
into	#capacity
from	master..sysusages u
where	u.dbid = db_id(@dbname)             
and	u.segmap <> 4 and u.segmap > 0                     -- anything but log only; this includes mixed data & log

if (lower(@type) = "all")
begin
insert  #capacity
select	convert(varchar(5), "log")
,	convert(numeric(15,6), isnull(sum(curunreservedpgs(u.dbid, u.lstart, u.unreservedpgs)),0)*@@maxpagesize/@Mb)
,	convert(numeric(15,6), isnull(1.0*sum(u.size)*@@maxpagesize/@Mb, 0))
from	master..sysusages u
where	u.dbid = db_id(@dbname)
and	u.segmap & 4 = 4 and u.segmap > 0                          --  log; this includes mixed data & log

insert  #capacity
select	convert(varchar(5), "total")
,	convert(numeric(15,6), isnull(sum(curunreservedpgs(u.dbid, u.lstart, u.unreservedpgs)),0)*@@maxpagesize/@Mb)
,	convert(numeric(15,6), isnull(1.0*sum(u.size)*@@maxpagesize/@Mb, 0))
from	master..sysusages u
where	u.dbid = db_id(@dbname)
and	u.segmap > 0
end

select	Type
,	Used = Allotted - Unused
,	Allotted
,	PercentFull = case when Allotted > 0 then convert(numeric(9,6), 100.0 * (Allotted - Unused) /  Allotted)
			   else 0.000000
		      end
from	#capacity
go

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