Why do buildings appear and disappear at different magnifications?

Some of the large buildings I added disappear when I zoom in; and some buildings only show up at one zoom level. Even stranger some buildings on one block only show up at like the 3rd highest zoom level and some buildings on the block across the street only show up at the 2nd highest zoom level.

Has anyone else this problem? Is it a problem with my browser or am I doing something wrong when I add the buildings. Thanks for any tips, ideas, pointers, etc