ldapmodify failing with large attribute

[Geoff Swan <gswan3@bigpond.net.au>]

I have a problem appearing where a large (16.6MB approx) value is to be
saved to an attribute (certificateRevocationList).
Prior to the value being this large, ldapmodify had no problems updating
it. However it appears to have crossed some magic threshold where it
will no longer be accepted, and aborts with: ldap_modify: Can't contact
LDAP server (-1)

The ldapmodify operation is being performed on the ldap host machine
using the ldap root user with simple password authentication.
Openldap version is 2.4.30 using back-bdb with Linux OS (2.6.32 64 bit).
There is no replication configured. It's a fairly simple setup.

I've seen a couple of similar threads alluding to the same problme,
however without any solution.
http://www.openldap.org/lists/openldap-software/200905/msg00062.html
http://www.openldap.org/lists/openldap-technical/201501/msg00006.html

I'm curious to know where the limit is that is causing the sudden
inability for ldapmodify to complete.
Nothing was immediately apparent after a quick look through some of the
source.
Also, if the issue is a known one, was it addressed in a newer release?

I can run the same test on a machine with openldap-2.4.40 to see if it
persists if that is of any help.

Thanks,
Geoff