[imp] SMIME support broken?

[Max-4004]

I did an upgrade from Horde 3.0 to 3.1 and IMP 4.0 to 4.1.
If I open an SMIME signed email I get:

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to 
allocate 1818838687 bytes) in 
/var/www/webapps/horde.new/htdocs/lib/Horde/SessionObjects.php on line 208

(tried to allocate 1,7 GB memory)

Even if the mail contains just a few words. With SMIME disabled the 
emails work fine.

Thx for the great Horde system!

Max