To reproduce:
Pre-Setup steps:
1) Open Control Panel
2) Switch to either Large or Small Icons
3) Select Region
4) Change Format to Slovenian and Apply

Post-Setup steps:
1) Create new project
2) Select either object in scene
3) Write a negative value in one of its position or rotation axes
4) Copy it
5) Try pasting it into any other field

Expected: It gets copied normally and affects object as supposed
Actual: It gets reverted to 0

Reproduced in 2017.1.0f1, 2017.2.0f3, 2017.3.0b8, 2018.1.0a3

Note: In 2017.1 and .2 versions there is a bigger issue. Trying to click "Static" checkmark on object with negative value creates even bigger issue breaking the whole inspector

Reproduced in Win7 fully. Not reproduced in Win10 in 2017.3+ versions