WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
On its own, no. This assumes the glass is clean and non-conducting (e.g. no gettering on it) so it doesn't matter where it lands. However, it may be a sign of a manufacturing fault which could cause trouble.