Not a bug. By choosing the only targeted mode at least once, the spell has become a targeted spell. And like all targeted spells, if all its targets have become illegal by the time it would resolve, it is removed from the stack, and none of its effects happen. This is a fundamental rule of fMagic.

608. Resolving Spells and Abilities
[...]
608.2b If the spell or ability specifies targets, it checks whether the targets are still legal. A target
that’s no longer in the zone it was in when it was targeted is illegal. Other changes to the game
state may cause a target to no longer be legal; for example, its characteristics may have changed
or an effect may have changed the text of the spell. If the source of an ability has left the zone it
was in, its last known information is used during this process. If all its targets, for every instance
of the word “target,” are now illegal, the spell or ability doesn’t resolve. It’s removed from the
stack and, if it’s a spell, put into its owner’s graveyard. Otherwise, the spell or ability will
resolve normally. Illegal targets, if any, won’t be affected by parts of a resolving spell’s effect
for which they’re illegal. Other parts of the effect for which those targets are not illegal may still
affect them. If the spell or ability creates any continuous effects that affect game rules (see rule
613.11), those effects don’t apply to illegal targets. If part of the effect requires information
about an illegal target, it fails to determine any such information. Any part of the effect that
requires that information won’t happen.