CouchDB "last_seq" number changes when adding since=now

Question

I am getting inconsistent results from CouchDB version 3.2.1.

If I get a list of changes in a database by calling http://docdb.mycouchdb.com/my_database/_changes I get a long list of changes in "results" with the final "seq" value matching what I get in "last_seq":

{"results":[
{"seq":"1-g1AAAABPeJzLYWBgYMxgTmEQTM4vTc5ISXIwNDLXMwBCwxygFFMiQx4Lw38gyMpgTmTMBQqxGxiaWRilJmHTkgUAFM4Udw","id":"_design/timestampsviews","changes":[{"rev":"1-72c0e9b448985fd65beb3cc3a580c588"}]},
.
.
.
{"seq":"330-g1AAAABSeJzLYWBgYMxgTmEQTM4vTc5ISXIwNDLXMwBCwxygFFMiQx4Lw38gyMpgTgIq9coFirIbGJpZGKUmYdOVBQBEcxTC","id":"fa3441f98a6643810cd8925d6491ef9f","changes":[{"rev":"1-88db0df4d97e2004c00c87c030bda7b5"}]}
],
"last_seq":"330-g1AAAABSeJzLYWBgYMxgTmEQTM4vTc5ISXIwNDLXMwBCwxygFFMiQx4Lw38gyMpgTgIq9coFirIbGJpZGKUmYdOVBQBEcxTC","pending":0}

However if I do http://docdb.mycouchdb.com/my_database/_changes?since=now (ie. add "?since=now") because I only want to get "last_seq" I get a completely different value which did not appear in the previous list:

{"results":[

],
"last_seq":"333-g1AAAABSeJzLYWBgYMxgTmEQTM4vTc5ISXIwNDLXMwBCwxygFFMiQx4Lw38gyMpgTgIq9c0FirIbGJpZGKUmYdOVBQBE2RTF","pending":0}

Any idea what is going on here? Is this a bug?

I would expect one of two things.

Surely either http://docdb.mycouchdb.com/my_database/_changes should have a couple more entries in "results" and end with "last_seq":"333-g1AAAABSeJzLYWBgYMxgTmEQTM4vTc5ISXIwNDLXMwBCwxygFFMiQx4Lw38gyMpgTgIq9c0FirIbGJpZGKUmYdOVBQBE2RTF"

or http://docdb.mycouchdb.com/my_database/_changes?since=now should end with "last_seq":"330-g1AAAABSeJzLYWBgYMxgTmEQTM4vTc5ISXIwNDLXMwBCwxygFFMiQx4Lw38gyMpgTgIq9coFirIbGJpZGKUmYdOVBQBEcxTC"

In other words, consistency ... so that "last_seq" is the same regardless of how you called it, or am I missing something here?