I got a U1253B (the Ole dmultimeter ) a few weeks ago. It has some strange behavior. When switching from ohms to mV the meter will read something like 1200 mV and this value will slowly creep upwards until it displays OL. Switching back to ohms shows a resistance in the order of 1000 ohm that creeps upwards until the meter switches ranges . then it goes very quickly to OL on the highes resistance range. Switching back to mV gives the same behavior. I need to switch to volts and back to mV before it behaves correctly.
Switching form ampere to pulse generator sometimes leaves the meter in ampere mode.
It's almost like the rotary switch has issues. I vaguele remeber having read this kind of problem before with this series of multimeters.
Unfortunately it sounds like the unit is defective. I would advise you to send the unit back to Agilent. Hopefully the unit is still under warranty. if you have further questions please forward to firstname.lastname@example.org