Ideally, there wouldn't be any movement. Is it hurting it? Hard to say...If its as mild as you describe, probably not but over time, it might advance some normal wear/tear issues a tad.

When you play standing, you inevitably place more weight upon the keyboard as you play...When you're sitting, its not as much.

I would suggest upgrading to a heartier kb stand.

I can't stand it if my KB jiggles around.

Bill in Dayton