From Patch 1.21 Notes:

[dev1302] The Action Subtargets option has been added to the Configuration menu, under Target Settings. Toggling off disables the selection of alternate targets for actions executed directly from the action bar; actions will instead be performed on the current target.
* Setting can also be toggled via a text command.
/subtarget（/st） [subcommand]
　>> Subcommands:
　on - Enable Action Subtargets
　off - Disable Action Subtargets
　Toggle between on and off when no subcommand is specified.
　* Enabled by default.

Basically, "/st off" should fix the issue.