I am reporting this bug here because bugs.gnome.org seems to be down.
Here is a repeatable scenario that crashes Dia 0.88.1:
Create a new diagram.
Choose "UML" notation.
Choose the "implements, class implements a specific interface" tool.
Click somewhere in the blank diagram to add the line-and-circle.
Type Ctrl-X in the diagram to attempt to cut this object out.
#0 0x403a7a1d in __strdup (s=0x0) at strdup.c:42
#1 0x40574d8f in implements_copy (implements=0x28f346d) at implements.c:354
#2 0x9999999a in ?? ()
Dia was installed from the 'dia-0.88.1-ximian.1' RPM package and
was running on a RedHat 6.2 system.
Pierre Sarrazin <sarrazip at sympatico dot ca>