Bluetooth device only try to pair Samsung Galaxy S3 but not HTC Sensation or Samsung Galaxy Nexus

Bluetooth device only try to pair Samsung Galaxy S3 but not HTC Sensation
or Samsung Galaxy Nexus

Bluetooth device supports Bluetooth 2.1 so no keying PIN necessary.
All 3 Android phones Samsung Galaxy S3 with Android 4.1.2, HTC Sensation
with Android 4.0.3 and Samsung Galaxy Nexus with Android 4.1.2 are running
the same app - BluetoothChat app by Google targeting Android API level 15
(4.0.3). 3 apps on 3 phones were listening to incoming connections (Serial
Port Profile I suppose) but only Samsung Galaxy S3 gets asked to allow or
disallow pairing. I've tried doing the same test with each individual
device and each pair of them but the result is the same.
Any ideas why this is happening?