pumping Q - medela harmony

I've been pumping a little... somewhat to ease engorgement, somewhat to build a small stash for going out or something. I got a medela harmony which works but I'm wondering if there's something I am missing because...

It doesn't "let go"! I pump, it sucks, and then it doesn't release. The suction does not break. This leads to my nipple feeling like it's being choked. I mean, it works. It doesn't hurt after, but shouldn't there be a release of sorts after each "suck" or pump or whatever?

x-posted