[imp] IMP5 hangs opening messages with multiple pdf attachments

[Peter Woit]

We've been using Horde/Imp for years, recently installed Horde4/Imp5. 
Everything seems to work fine (traditional, not dynamic interface), 
except for one major problem: when a user tries to open certain e-mail 
messages their session hangs, and they have to restart their browser.

This is completely reproducible, the messages that cause the problem 
seem to be ones with multiple pdf attachments.

The problem leads to a lot of hung-up httpd processes, which when killed 
give an error message to the log of

zend_mm_heap corrupted

Running apache with USE_ZEND_ALLOC=0 doesn't fix the problem, but just 
causes that error message to not be there when the httpd is killed.

Nothing unusual shows up in horde or apache logs.

Perhaps the problem has to do with how IMP is handling pdf attachments, 
but I don't see any way to change its behavior to test this.

Any advice about what to try, or how to generate enough debugging info 
for a useful bug report, would be appreciated.

Peter Woit