Steps to reproduce:
1. Select a theme that uses the smooth egine
2. Start gtk-gnutella (for example)
3. 


Stack trace:
        GNU gdb 6.6
        Copyright (C) 2006 Free Software Foundation, Inc.
        GDB is free software, covered by the GNU General Public License,
        and you are
        welcome to change it and/or distribute copies of it under
        certain conditions.
        Type "show copying" to see the conditions.
        There is absolutely no warranty for GDB.  Type "show warranty"
        for details.
        This GDB was configured as "i686-pc-linux-gnu"...
        Using host libthread_db library "/lib/libthread_db.so.1".
        (gdb) run
        Starting
        program: /home/ubrpngn/build/gtk-gnutella-0.96.3/src/gtk-gnutella 
        [Thread debugging using libthread_db enabled]
        [New Thread -1208277328 (LWP 22639)]
        07-02-18 21:01:16 (WARNING): This is an unofficial build which
        accesses files in this directory:
        "/home/ubrpngn/build/gtk-gnutella-0.96.3"
        07-02-18 21:01:16 (MESSAGE): language code: "en"
        07-02-18 21:01:16 (MESSAGE): using locale character set "UTF-8"
        07-02-18 21:01:16 (MESSAGE): primary filename character set
        "UTF-8"
        07-02-18 21:01:16 (MESSAGE): gtk-gnutella/0.96.3 (2006-11-09;
        r12293; GTK2; Linux i686)
        07-02-18 21:01:16 (MESSAGE): D-BUS set up and ready for use.
        07-02-18 21:01:16 (MESSAGE): Sent D-BUS signal 'Events': started
        07-02-18 21:01:16 (WARNING): can't read file
        "/home/ubrpngn/.gtk-gnutella/config_gnet": No such file or
        directory
        [New Thread -1213371504 (LWP 22644)]
        [New Thread -1221764208 (LWP 22645)]
        [Thread -1213371504 (LWP 22644) exited]
        [Thread -1221764208 (LWP 22645) exited]
        07-02-18 21:01:16 (WARNING):
        gnutls_certificate_set_x509_key_file() failed: Error while
        reading file.
        07-02-18 21:01:16 (WARNING): [hosts] unable to retrieve: no
        alternate locations known
        07-02-18 21:01:16 (WARNING): [hosts] unable to retrieve: no
        alternate locations known
        07-02-18 21:01:16 (WARNING): [hostile IP addresses (private)]
        unable to retrieve: no alternate locations known
        07-02-18 21:01:16 (WARNING): [Spam database] unable to retrieve:
        no alternate locations known
        07-02-18 21:01:16 (WARNING): can't read file
        "/home/ubrpngn/.gtk-gnutella/sha1_cache": No such file or
        directory
        07-02-18 21:01:16 (WARNING): [download mesh] unable to retrieve:
        no alternate locations known
        07-02-18 21:01:16 (WARNING): [banned mesh] unable to retrieve:
        no alternate locations known
        07-02-18 21:01:16 (WARNING): [Host Whitelist] unable to
        retrieve: no alternate locations known
        07-02-18 21:01:16 (WARNING): [PARQ upload queue data] unable to
        retrieve: no alternate locations known
        07-02-18 21:01:16 (WARNING): can't read file
        "/home/ubrpngn/.gtk-gnutella/config_gui": No such file or
        directory
        
        Assertion failure (halloc.c:75) "value"
        
        Program received signal SIGABRT, Aborted.
        [Switching to Thread -1208277328 (LWP 22639)]
        0xb7fe0410 in __kernel_vsyscall ()
        (gdb) bt full
        #0  0xb7fe0410 in __kernel_vsyscall ()
        No symbol table info available.
        #1  0x4120fb97 in raise () from /lib/libc.so.6
        No symbol table info available.
        #2  0x4121114e in abort () from /lib/libc.so.6
        No symbol table info available.
        #3  0x00000002 in ?? ()
        No symbol table info available.
        #4  0x00000000 in ?? ()
        No symbol table info available.
        (gdb) cont
        Continuing.
        
        Program terminated with signal SIGABRT, Aborted.
        The program no longer exists.

Other information:
gtk-gnutella is the application that brought this to my attention; the problem may exist with others as well.
I know the stack trace is practically worthless, but for some reason it's the best I can get - even when compiled with -O1 -gddb.
More detailed information can be found on the gtk-gnutella mailing list, where I started working on this: http://sourceforge.net/mailarchive/forum.php?thread_id=31686242&forum_id=5941