Fatal Error: Out of Memory

I keep getting this error (with different numbers/files/lines) in the dashboard widgets. I also get it when I try to upgrade WP from within the admin panel (as opposed to manually via ftp), and sometimes (but not always) if I try to install or upgrade a plugin.

Fatal error: Out of memory (allocated 22282240) (tried to allocate 1245184 bytes) in /home/homework/public_html/wp-includes/class-simplepie.php on line 5410

As far as I can tell, there is no one specific plugin causing the problem. If I uninstall enough of them, the problem goes away, but it doesn’t seem to matter which ones. Once or twice it got bad enough that the errors appeared on the public side of the blog.

The errors don’t make sense to me, for several reasons.

1) The amount of memory allocated is often, if not always, greater than the amount the system says it attempted.

2) By default, I should have 32MB memory. This was confirmed by my host, and by a memory-usage plugin.

3) The memory-usage plugin says my highest usage was 21.72. Obviously, this is less than 32 MB, so I shouldn’t have an issue.

4) Even with the adjustments from this page, or similar ones suggested elsewhere, used to bump up the allowable memory to 128MB, I still get the errors. Even if it did, I think this would be a “band-aid” fix, rather than a real solution.

There seems to be some kind of bug, or database error, or something besides plain old memory usage. Can anyone shed some light on this, or tell me where I might start to find some real answers? (I have talked to my host. The host’s conclusion was the same as mine – that it isn’t a memory issue, but a bug or something.)

If it helps any, I have several other WP blogs with the same host, and none of them have this problem. (None of them have quite as many plugins, either, but they do all have multiple plugins.)