Haven't encountered this myself, but I would consider a couple of things:
- The fill in the plan is the correct size, but when you draw it in your master layout it is 1:1, so may be scaling itself to a larger fill and you're just seeing a little bit of it
- Check your work environment settings to make sure you have unchecked the uniform color for Master items on layouts (Work Environment > User Preference Schemes > On-Screen Options)
Hope this helps