The "Enable Perforce Integration" setting is not saved/restored from the Registry.
A quick scan through the code suggests that in Config.cs, PerforceEnabledPrefName is unused. This appears to be related to the inability for you to disable Perforce Integration using the Perforce Settings > Enable Perforce Integration checkbox.
Perforce server version "p4 -Ztag info"
: ... serverVersion P4D/NTX64/2014.2/978861 (2014/12/19)
P4Connect release (look at the bottom right corner of the Perforce Configuration window)
: P4Connect 2.7 betaR.12101
: Unity 5.0.0b22 (32 bit)
Operating system version, 32bit or 64bit
: Windows 7, SP1, 64 bit.