FSL 8w EOL on HF Matchbox - Cathodes Melts

[BC5-80]

You meaning: When only one wire connected to each end of the lamp, it will run most EOL lamps to vacuum loss?

The ballast will require filament continuity at both ends of the lamp to sustain self-oscillation because they form part of the circuit. When one end burns out, the oscillator stalls. If you were to short out the open-circuit filament, the oscillator will work until something else fails. In a throw-away CFL, often a transistor fails short-circuit and blows the in-line fuse.