This is occurring because you have other morphs (perhaps an injected character?) also applied.

When you spawn a morph, ALL changes to the geometry are merged into that single morph. When you turn up the spawned morph, you are getting all of the morph settings from the other changes DOUBLED.

There are several solutions to this:

1. Use the morph brush. It's changes are controlled by the "custom morph" dial that will be automatically added.

2. Set up your magnet. Click on the REM posed for your injected character. Spawn the morph. Delete the Magnet. Re-inject the character. Turn the morph dial to 1.

Hope this helps.