bug, bad memory, or bad disk?

We have a Postgres server (PostgreSQL 9.1.6 on x86_64-unknown-linux-gnu, compiled by gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3, 64-bit) which does streaming replication to some slaves, and has another set of slaves reading the wal archive for wal-based replication. We had a bit of fun yesterday where, suddenly, the master started spewing errors like:

2013-02-13T23:13:18.042875+00:00 pgdb18-vpc postgres[20555]: [76-1] ERROR: invalid memory alloc request size 1968078400
2013-02-13T23:13:18.956173+00:00 pgdb18-vpc postgres[23880]: [58-1] ERROR: invalid page header in block 2948 of relation pg_tblspc/16435/PG_9.1_201105231/188417/56951641
2013-02-13T23:13:19.025971+00:00 pgdb18-vpc postgres[25027]: [36-1] ERROR: could not open file "pg_tblspc/16435/PG_9.1_201105231/188417/58206627.1" (target block 3936767042): No such file or directory
2013-02-13T23:13:19.847422+00:00 pgdb18-vpc postgres[28333]: [8-1] ERROR: could not open file "pg_tblspc/16435/PG_9.1_201105231/188417/58206627.1" (target block 3936767042): No such file or directory
2013-02-13T23:13:19.913595+00:00 pgdb18-vpc postgres[28894]: [8-1] ERROR: could not open file "pg_tblspc/16435/PG_9.1_201105231/188417/58206627.1" (target block 3936767042): No such file or directory
2013-02-13T23:13:20.043527+00:00 pgdb18-vpc postgres[20917]: [72-1] ERROR: invalid memory alloc request size 1968078400
2013-02-13T23:13:21.548259+00:00 pgdb18-vpc postgres[23318]: [54-1] ERROR: could not open file "pg_tblspc/16435/PG_9.1_201105231/188417/58206627.1" (target block 3936767042): No such file or directory
2013-02-13T23:13:28.405529+00:00 pgdb18-vpc postgres[28055]: [12-1] ERROR: invalid page header in block 38887 of relation pg_tblspc/16435/PG_9.1_201105231/188417/58206627
2013-02-13T23:13:29.199447+00:00 pgdb18-vpc postgres[25513]: [46-1] ERROR: invalid page header in block 2368 of relation pg_tblspc/16435/PG_9.1_201105231/188417/60418945

There didn't seem to be much correlation to which files were affected, and this was a critical server, so once we realized a simple reindex wasn't going to solve things, we shut it down and brought up a slave as the new master db.

While that seemed to fix these issues, we soon noticed problems with missing clog files. The missing clogs were outside the range of the existing clogs, so we tried using dummy clog files. It didn't help, and running pg_check we found that one block of one table was definitely corrupt. Worse, that corruption had spread to all our replicas.

I know this is a little sparse on details, but my questions are:

1. What kind of fault should I be looking to fix? Because it spread to all the replicas, both those that stream and those that replicate by replaying wals in the wal archive, I assume it's not a storage issue. (My understanding is that streaming replicas stream their changes from memory, not from wals.) So that leaves bad memory on the master, or a bug in postgres. Or a flawed assumption... :)

2. Is it possible that the corruption that was on the master got replicated to the slaves when I tried to cleanly shut down the master before bringing up a new slave as the new master and switching the other slaves over to replicating from that?