Bug in fast route-finding?

This:

[code]“Relations” by Matt Weiner

Lab is a room.
A theme is a kind of thing. Love is a theme. Loss is a theme. Lust is a theme.
Suggesting relates various themes to each other. The verb to suggest (he suggests, they suggest, he suggested, it is suggested, he is suggesting) implies the suggesting relation. Love suggests Loss. Loss suggests Love. Loss suggests Lust. Lust suggests Loss.

Every turn: say “[The next step via the suggesting relation from Love to Lust].”[/code]

behaves as expected; every turn it will print “Loss.”

But add fast route-finding, thus:

[code]“Relations” by Matt Weiner

Lab is a room.
A theme is a kind of thing. Love is a theme. Loss is a theme. Lust is a theme.
Suggesting relates various themes to each other with fast route-finding. The verb to suggest (he suggests, they suggest, he suggested, it is suggested, he is suggesting) implies the suggesting relation. Love suggests Loss. Loss suggests Love. Loss suggests Lust. Lust suggests Loss.

Every turn: say “[The next step via the suggesting relation from Love to Lust].”[/code]

and it prints “Class” every turn.

Anyone got ideas before I head to the bug tracker? (And, where on earth does “Class” come from?)

Reported as issue 578.