Thank you for your post!
Testing and Development is aware of this issue in FileMaker Pro 14 and 15. There are no work arounds at this time (aside of maybe using FileMaker Go). When further information is available I will post back here!
There are some workarounds...like changing calc fields to auto-enters or using separate fields for find mode (either local or globals). Not satisfactory, but an answer.
This issue has been addressed in FileMaker Server 16.