To reproduce:

1. Download and open attached "DPI_Test_unity5.5.0f3.zip" project.
2. Build and run the project on high DPI phone.

Expected result: when clicking the button, only click is triggered. Drag function is not triggered when pressing the button.
Actual result: when clicking the button, sometimes drag and click are both triggered at the same time.

Reproduced with: 2018.1.0a5, 2017.3.0b10, 2017.2.0p2, 2017.1.2p3, 5.6.3p4, 5.5.5p1.

Devices Under Test:

Samsung SM G928F*, OS:7.0, CPU:arm64-v8a, GPU:Mali-T760,
Build:samsung/zenltexx/zenlte:7.0/NRD90M/G928FXXU3CQG2:user/release-keys (560 DPI)

Verizon SM G930V*, OS:6.0.1, CPU:arm64-v8a, GPU:Adreno (TM) 530,
Build:Verizon/heroqltevzw/heroqltevzw:6.0.1/MMB29M/G930VVRU2APG3:user/release-keys (640 DPI)

Google Pixel XL*, OS:8.0.0, CPU:arm64-v8a, GPU:Adreno (TM) 530,
Build:google/marlin/marlin:8.0.0/OPR6.170623.012/4283428:user/release-keys (560 DPI)

Notes: Issue is more likely to appear on high DPI phones (500-700) DPI . Did not reproduce with iPhone 6 Plus 8.0 (401 DPI).