minnapple - what are your conclusions from this?
I would say that when you removed the 301 you cut a connection and caused a re-index of your site. When you added the link(s) you just caused more gbots to visit.
There are several googlebots and there are different functions.
some just collect links some spider pages some check for tos violations, and they all modify the index with the info they gather.
So maybe when the 301 was removed site b was being crawled (as what was moved) then the 301 was taken away so that crawl was cleared as (this site is now 1 page) then the link said 'hey here is an entirely new site yum over 400 pages'. Then a few more links caused a few more googlebots to join in the fun.
My guess and from reading different posts on WW is that.
1st googlebot(s) crawls site and lists links only and makes somewhat of a sitemap of the site along with a list of outbound links for each page. it then adds this info to an internal google database.
2nd googlebot(s) crawls pages listed in the database and adds them to the index, caches them etc.