Why do the commands table and table twoway with the option markvar(newvar)create the error "__000001 not found r(111);"? The error occurs in Stata/MP 18.0 for Windows (64-bit x86-64) and also in Stata/MP 17.0 on the same platform.

Code:
. use https://www.stata-press.com/data/r18/nhanes2l, clear
(Second National Health and Nutrition Examination Survey)

. table sex, markvar(mynewvar)

---------------------
         |  Frequency
---------+-----------
Sex      |           
  Male   |      4,915
  Female |      5,436
  Total  |     10,351
---------------------
__000001 not found
r(111);

. noisily table sex diabetes, markvar(mynewvar2)

--------------------------------------------
         |           Diabetes status        
         |  Not diabetic   Diabetic    Total
---------+----------------------------------
Sex      |                                  
  Male   |         4,698        217    4,915
  Female |         5,152        282    5,434
  Total  |         9,850        499   10,349
--------------------------------------------
__000001 not found
r(111);

. tab mynewvar mynewvar2, missing

           |       mynewvar2
  mynewvar |         0          1 |     Total
-----------+----------------------+----------
         1 |         2     10,349 |    10,351 
-----------+----------------------+----------
     Total |         2     10,349 |    10,351
The Stata 18 help files say:
markvar(newvar) generates an indicator variable that identifies the observations used in the tabulation
.

Yes, the table and table twoway option markvar(newvar) does what the help files say but why does it also create an error? It is possibly my user error (despite being a long-time user-programmer),