Yes, there's a limit and this issue has been previously reported.
For More Information see: Relationship Graph elements disappear beneath certain height
This is one of many acknowledged bugs that can be found in the Known Bug List here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: http://www.4shared.com/file/8orL8apk/FMP_Bugs.html
Thank you for your post.
The information and link provided by "PhilModJunk" is correct (Thank you!).
I have attached your post to the original reported issue so that our Development and Software Quality Assurance (Testing) teams can take notice of your screen shot.