There's a note in Apprentices (pg 54) that:
The apprentice’s Virtues and Flaws affect the Lab Total, as do his parens’. For example, an apprentice with Inventive Genius adds to the Lab Total, while Waster of Vis imposes twice the normal vis cost. All laboratory-related Virtues and Flaws apply. If both parens and apprentice have Waster of Vis, for example, the laboratory activity costs twice the normal amount of vis.
I'd taken that as meaning that any virtue/flaw that would affect the lab total if the master had it would also affect the lab total, in the same way as though the master had it (so for example, a deficiency in an Art would halve the Lab Total, and a Focus would double the leading magus' lowest relevant Art).
However, when I mentioned the idea on Discord, @OneShot thought (as I understood them) that the definition of a "laboratory-related" virtue and flaw was narrower than that, in that it should be something that specifically affected lab work, and also that virtues/flaws that affected Arts would be meaningless as they would affect the assistant's Art scores, which weren't being used in the first place.
Is there a clear-cut right/wrong answer to this? If not, what's the best interpretation?