The UK recommendation is to hold the release during the start of a winch launch, due to the exceptionally short time available to avoid disaster by releasing if a wing is going down and you cannot prevent it with aileron. While this may not apply to an aerotow launch it is likely that pilots trained on the winch and flying unflapped gliders would do the same for an aerotow launch. I would expect pilots to take their hand off the release once comfortably clear of the ground. I have not heard of an inadvertent release.