Oppss it's even worse??? I thought it was an OLED LCD 5 years is a young meter as long as you don't expose much heat, it will last more years. Currently working with two U1251 A /B models at work and one (A) of them has the plastic of the rotary switch ripped off ( maybe too exposure to sunlight).
Sunlight and heat destroy anything. Last summer I was fixing my pool equipment and my trusty Fluke 27/FM was under the sunlight for about 15min or so. It was facing down when I was not using it, so the LCD wouldn't become dark but, even still, its display became faded. It only came back to normal when I reseated and cleaned the zebra strips.
One thing i've noticed at home during some experiments with electronics using AC 230V with isolation transformer, the meters BM235 e UT139A measuring V / A ( vice-versa) of the circuit. would display OL when mangled the contacts from old plugs. it does create arcs and maybe AC transients in lower energy (about 6VA ) and trigger the OL situation on the meter. It doesn't matter if i swap the meters for A and other for V . To disable the OL of course it is required to turn off. the units.
I didn't repeat the experience to avoid any potential damage to meter or DUT or even me and used better plugs.
is this some sort of protection implemented on the meters?
I suspect the arcs may be shooting the voltage to very high levels. That or the meters are susceptible to high frequency transients.
Some meters, even from reputable manufacturers such as HPAK, showed this behaviour. The major issue is that there are usually several tradeoffs when designing the input section of a multimeter: safety level, noise/sensitivity, bandwidth...
This is only solved by a very good and well tested design.