Using Rear Diff Lock And Shifting From H4 To L4

Dear Sir, I actually have a problem with the shifting of H4 to L4 and using the Diff Lock on my Land Cruiser. When I engage the 4x4 button I get the 4WD H4 without a problem and can shift to L4 easily; however, when I engage the Diff Lock button, I am unable to disengage the system and have to turn off the car and restart it to disengage the Diff Lock. Also, have a hard time shifting back from L4 to H4 at times as it does not disengage from L4. When I turn off the car in H4 while gears are in L4, I turn the knob to L4 and back to H4 to resolve the issue after restarting the car. This seems a bit odd. Questions is that am I doing anything wrong when engaging the systems which I cannot disengage later?