Malfunctioning Event Modification Filter?

[intelligentdb 0]

I’m working in an Event folder with only 5 events.
Today is 2020-10-10
My filter (gFilterLastModified_ts) is a timestamp field.
When I use
PCGM_FilterByLastModified ( gFilterLastModified_ts ) or use
PCGM_FilterByField (‘UpdatedMin” ; gFilterLastModified_ts )
with the value “2020-10-10 2:09:09 PM” for example,
my results show two events, Updated
"2020-10-10 11:11:03 AM” and
“2020-10-10 12:36:53 PM”

or with the value “2020-9-15 1:53:53 PM” for example,
my results show all 5 events, including the one Updated
“2020-09-13 1:40:34 PM”

How and Why?

Set Variable [ $result; Value:PCGM_OpenFolder( SYSTEM::gFolder ; "Calendar" ) ]
Set Variable [ $result; Value:PCGM_FilterByLastModified( SYSTEM::gFilterLastModified_ts ) ]
Set Variable [ $result; Value:PCGM_GetFirstRecord ]
Loop
…
Set Variable [ $result; Value:PCGM_GetNextRecord ]
End Loop

Thanks.