They're well known for siphoning fuel from Gaza hospitals and lobbing rockets at Israeli ones. So even if they hadn't already been doing this regularly it would still be unsurprising to find Hamas soldiers using hospitals and mosques as military facilities:

The Shin Bet head added that many of Hamas's senior activists were hiding out in mosques and hospitals in Gaza, some of them in the guise of doctors and male nurses. "Some of them have turned dozens of mosques into command and control centers on the assumption that Israel won't attack those places," he said. "Their development laboratories have been completely destroyed. Their tunnel system has sustained heavy damage. Hamas is trying to utilize [what remains] so that their operatives can escape to Egypt."

I like the Jason Bourne-esque touch of returning to the mosques where they were first brainwashed. Kind of gives the whole thing much-needed narrative unity, I think. Of course using religious sites for military purposes has been a violation of the rules of warfare for the entire breadth of human civilization. But whatever.

References:
* Hamas Intentionally Creating Humanitarian Crises In Gaza By Stealing Fuel From Hospitals For Their "Operations" Against Israel [MR]
* Palestinians Firing Missile Barrages At Israeli Hospitals Treating Gaza Residents (Plus: Israeli Response Somewhat Underwhelming, Constrained) [MR]
* Palestinians Commit Several War Crimes in Just a Few Hours. Instead of Reporting That, Reuters Publishes Gripping Tale of Glorious Palestinian Martyrdom (and We're Not Even Exaggerating About That...) [MR]
* Diskin: Hamas dealt a 'serious blow' [JPost]
* Hamas's Militarized Mosques Not Immune From Israeli Jets [MR]

Previously:
* Hamas Now Doing Everything Humanly Possible To Generate Gaza Civilian Casualties
* Iran Orders Every Muslim In The World To Attack Israel
* Anti-Israel Photojournalists Struggling To Cope With Extensive Israeli Humanitarian Measures, Low Palestinian Collateral Damage