You cancel it, clear up what you don't want locally on the phone and watch it happen again as a new album is added on iTunes.
What is odd is that it appears to be a state within the iCloud music library. For instance, after I had enabled match on my phone and then cleared up, as above, last night I enabled match on my iPad. This did not download all the new material that was new to match (from my MBP) like my phone did. It only automatically downloads new material, uploaded since re-subscribing to match, albeit on both devices.
I'm not fussed about the internal logic of how it decides what's new and which devices get it, that bit is probably correct. What is the bug is the ignorance of the switch designed to prevent automatic downloads.