Bug 292789 currently blocks exactly one (private, security-sensitive) bug. Attempting to view the dependency graph for it results in a 500 Internal Server Error after attempting to load the page for a while. From the outside it appears the script execution time exceeded a global maximum imposed by either the Perl or server configuration, although this is just speculation. Given the small data set, I suspect the code enters an infinite loop somewhere (but that's also just speculation).
WFM on 2.20 (landfill). The dependency graph is known to be broken on b.m.o. This should be fixed on the next upgrade.