Thanks, if anyone has seen this sizing issue or knows how to prevent this going forward.
Stamps don't get resized when applied. My guess is that the page you're placing them on is very large, so they look small.
Compare the page size and zoom level of both files when applying the stamp to them.
This can happen if you move the mouse slightly at the time you click to apply the stamp. The fix is to not move the mouse.
BTW, to replicate this, select the stamp tool and click and hold the mouse button down, and with the button held down drag out a rectangle. You will see that you can set the size of the stamp to whatever you want. In the case where the stamp appears very small, this process happens so fast you don't notice and think all you've done is clicked, but you've actually clicked and dragged a very small amount.
So doing that we were able to readily replicate. Is there a way to turn this "feature" off? The users who semi-regularly run into this move very fast when going through and stamping documents, and would like for this to simply not happen.
Sorry, I'm not aware of a way to disable or adjust the sensitivity of this.