FYI, this is what I have read in Foxpro Advisor Magazine

CREATE TABLE test (f1 C(10))

FOR i = 1 TO 12
APPEND BLANK
ENDFOR

SET TALK OFF
INDEX ON f1 TAG f1
? _TALLY && in VFP result is 0, FP2.X result is 12

SET TALK ON
INDEX ON f1 TAG f1
? _TALLY && result is 12 in all versions

According to the documentation, you need to set talk on/off for the _TALLY function to work so maybe if you set talk on it will work.
The _TALLY is supossibly allways filled when using SQL-SELECTS.