Steps to reproduce:
1. Create new material
2. Switch to Inspector Debug mode
3. Try to edit any string value in arrays (e.g. "String Tag Map" Element 0)

Actual result: For each letter added a new entry is created or older ones are replaced (see attached image)
Expected result: Value is changed

Tested and reproduced on:
Windows 10
Unity 5.2.4p1, 5.3.3f1, 5.4.0b7

Not reproducible in:
Unity 5.1.4f1

Note: On 5.1.4f1 it is reproducible but only on corrupted elements, on fresh elements it is not