[imp] problem with splited mails - found only 0 of 4 parts

[Jakob Lenfers]

Hi,

I've upgraded recently to horde3.1 with imp4.1. The rest is a debian 
stable with php 4.3.10, apache 2.0.54. The upgrade ran smoothly, but 
we've got a problem since then:

When user get big mail, splitted, imp can't open them anymore. It only 
displays an error: "Can not display - found only 0 of 4 parts of this 
message in the current mailbox."

The 4 messages are in the same mailbox and my Gnus can open them perfectly.

A google search with parts of the error-message revealed nothing. 
Perhaps anyone here knows something. TIA.

Jakob