I finally found confirmation that Hamas has been executing "collaborators" during this operation in the Palestinian Arab press, although they do not give any numbers nor do they say that the victims were exclusively Fatah as the earlier Jerusalem Post story indicated.
There is one specific report of Hamas executing a 76-year old Fatah member and injuring his son, a woman and child because the man didn't adhere to his "house arrest."
For the purposes of my counting of Palestinian Arab on Arab deaths (the "self-death count") there is of course no way to know how many civilians are being killed by Hamas during the urban fighting with Israel. It is fair guess that Hamas is not nearly as concerned about Gaza civilian deaths as Israel is, and more than likely that Hamas craves such deaths so it can blame Israel. For example, yesterday's Guardian said that ten children were killed in Hamas-IDF battles - but who actually killed them? Similarly, there were at least three separate instances of Qasssams falling short in Gaza, killing two children and injuring others, in the thre days before Cast Iron started. How many of the hundreds of missiles since then have also fallen short, killed people and then Israel was blamed? One possible example is this story from Maan about a girl who was injured by a "missile" supposedly from an air strike; but how probable was it to have been an errant Qassam? We'll never know for sure, but it seems to me that the chances for Qassams falling short increase dramatically when the people launching them are in a very big rush to shoot it and disappear as quickly as possible. For now, though, I am only adding one to the 2009 self-death count, raising it to 37.
Another Arab source has an intriguing report, that Israel warned Syria that if Hezbollah tried to open a second front against Israel. Israel will hold Syria responsible - and attack the Syrians. Syria typically uses proxies to do its dirty work, but it is deathly afraid of anything that might destabilize the regime, so this makes a lot of sense.
There are reports that Israel arrested an Iranian reporter in Jerusalem for not adhering to Israeli military censorship.