Because an opposition minister moved to delay the vote that meant (a) filibustering while bringing everyone back to the chamber, (b) this then triggered an instant vote on the actual business, rather than them being able to continue the debate.
How on earth is this a sensible system?
Incidentally, I discovered recently that all of the votes at the Scottish Parliament happen together, in the evening. Debates happen earlier in the day on a range of subjects, and they can turn up to whichever ones they have an interest in - but they don't have to basically hang about all day to register their votes, they just have to make sure they're there for all of the votes at the end of the day. A much more efficient use of their time.
Original post on Dreamwidth - there are comments there.