When a discharge tube is used on a circuit that has a DC voltage component, there is a phenomenon occurs, called holdover, where the discharge in the tube continues being driven by the current from the power supply even after the surge voltage has subsided.
When a holdover occurs, for example when it is occurs in the drive circuit of a CRT, the screen darkens and discharge in the absorber continues, which can lead to the glass tube melting, smoking or burning.