Steps to reproduce

[Convert]::ToString(0xFFFFFFFFFFFF -band 0xFF0000000000,2)
[Convert]::ToString(0xFFFFFFFFFFFF -band 0x00FF00000000,2)
[Convert]::ToString(0xFFFFFFFFFFFF -band 0x0000FF000000,2)
[Convert]::ToString(0xFFFFFFFFFFFF -band 0x000000FF0000,2)
[Convert]::ToString(0xFFFFFFFFFFFF -band 0x00000000FF00,2)
[Convert]::ToString(0xFFFFFFFFFFFF -band 0x0000000000FF,2)

Expected behavior

111111110000000000000000000000000000000000000000
1111111100000000000000000000000000000000
11111111000000000000000000000000
111111110000000000000000
1111111100000000
11111111

Actual behavior

111111110000000000000000000000000000000000000000
1111111100000000000000000000000000000000
111111111111111111111111000000000000000000000000
111111110000000000000000
1111111100000000
11111111

Environment data

> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      5.1.15063.413
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.15063.413
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1