This seems to be a 2-year old bug: http://forums.cardhunter.com/threads/randimar-taking-the-week-off.4914/page-2#post-49411 Will Randimar's reset on the 1st and 2nd of Jan (in the US at least) this year?
A very good, and timely question! I hope we get a good answer. Edit: I obviously wrote this before I refreshed CH. Three years running for this bug. (It is definitely NOT a feature.) Very disappointing.
Actually, the fix would probably look like: if yesterdays_week <> todays_week then restock (IIRC, the bug was that it was only restocking when the week value increased.)