How to reproduce:
1. Create a new project
2. Open the Profiler window (Window -> Analysis -> Profiler)
3. Change the Profiler Modules so that only the 'Memory' Module is displayed
4. Create a new Script in the Project window
5. Right-click on the newly created Script and select 'Reimport'
6. Switch to 'Detailed' information type in the Profiler instead of 'Simple'
7. In the Profiler window press 'Take Sample Playmode' or 'Take Sample Editor'
8. Expand 'Scene Memory' -> 'Material'

Expected result: 'Hidden/Preview Transparent' did not use any additional memory after reimporting the Script
Actual result: one (2018.4) or three (2019.4+) additional instances of 'Hidden/Preview Transparent'' each used 1.2 KB or 1.1 KB of memory

Reproducible with: 2018.4.29f1, 2019.4.15f1, 2020.1.14f1, 2020.2.0b11, 2021.1.0a5

Notes:
The issue does not occur when reimporting Scripts while the Profiler window is closed since reopening the Editor. If the Profiler is opened and closed, the issue reproduces again