farmerswife is designed to work with an standard definition of 96 DPI (in Windows Vista) / 100% (Windows 7 = Default on installation). Increasing the text size (usually related with accessibility changes) will produce these kind of problems throughout the whole application.
On Windows (7, 8, 10) if the Display Scaling is set to 125% (Standard) some Buttons/icons overlap (Expand icons on Custom Fields, Toolbox > Settings > Display, Toolbox Selector tabs, Booking window fields) or "disappear" (Project report icon, Expand icons on Custom Fields).
If set to 100% they look fine.
We may be able to fix the problem on a case by case basis only if it's a big issue as it's not possible to add one general fix for the problem. If you encounter issues please set the setting to 100%.