I would guess that this is a file that has been converted from the .fp7 to the .fmp12 format as I have only seen this with buttons created prior to the format conversion. It is a known issue though FileMaker Inc. does not classify it as a bug.
For More Information see: Buttons spontaneously change size and position when a text style is applied
This is one of many acknowledged bugs that can be found in the Known Bug List thread here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: https://www.dropbox.com/s/jt09b82i0xijbu3/FMP%20Bugs.zip