REST Itemcount with date filter does not work?

The following returns 20 items from a discussion list

https://webapp1/_vti_bin/ListData.svc/DiscussionsList/$count?$filter=((Created ge datetime'2018-01-01T00:00:00Z') and (Created le datetime'2020-12-31T00:00:00Z'))

however the following returns the count of all items in the list which is 25 in my case

https://webapp1/_api/web/Lists/getbytitle('Discussions%20List')/ItemCount?$filter=((Created ge datetime'2018-01-01T00:00:00Z') and (Created le datetime'2020-12-31T00:00:00Z'))

Not sure if this is REST limitation. please advise. Thanks