Your trailer ceiling lights are 12VDC items and are powered by your on-board converter/charger unit and trailer battery as shown in this typical 30AMP RV wiring configuration.
What you are seeing is the on-board converter/charger unit jumping up in its DC VOLTS output which can be verified by using a multimeter across the battery terminals. The ON-BOARD CONVERTER/CHARGER normally puts out 13.6VDC most of the time and can increase to 14.4VDC when in boost charging mode if it has SMART MODE CHARGING technology.
This is determined by the battery which may be boiling out battery fluids (A bad thing) and is demanding BOAST 14.4VDC CHARGE mode from your on-board converter/charger.
I would check the DC VOLTAGE being supplied by the on-board converter/charging unit and the battery fluid levels in your connected 12VDC battery system.
If your on-board converter/charger unit is single mode type charger than it will "ALWAYS" only put 13.6VDC when on shore power which is right on the edge of making batteries boil-out fluids over time. You should be checking your battery fluids on a scheduled basis of at least every two weeks as if the fluids drop below the cores inside the batteries they will start self destruction and you will have to replace the batteries if not not caught quick enough.
Just my thoughts