How to reproduce:
1. Open the attached "Test" project and "Scene"
2. Observe "PrefTest" script, note that two PrefrenceItem attributes are used with two static functions nearby them. [PreferenceItem("Preferences B")] static method has a public access modifier, while [PreferenceItem("Preferences A") static method does not have any access modifier (is private by default)
3. Go to Edit --> Preferences

Expected result: Sections are created for both [PreferenceItem("Preferences A")] and [PreferenceItem("Preferences B")
Actual result: Only one preference section is created only for [PreferenceItem("Preferences A")] that is private by default

Regression introduced in - 2017.3.0a5
Reproducible with - 2018.1.0a1, 2017.3.0b4, 2017.3.0a5
Not reproducible with - 2017.3.0a4, 2017.2.0f3,

Note: Preference section is created if using protected access modifier