Optional Global INI File
MQ2Melee also has 3 global (not character specific) parameters that can be set in a second, optional INI file. MQ2Melee uses default values for these parameters unless it finds a file named MQ2Melee.ini that you created in the same directory. Here is an example of a MQ2Melee.ini file and a description of the parameters:
[Settings]
SpawnType=10
MeleeKeys=z
RangeKeys=x
Unless you have set up the said INI file, you can turn the plugin's melee or range attack on and off using the above listed keys.
The plugin itself does not have a target lock persay that I know of. You can run just the plugin, and it will only autoattack when told to. If you switch targets it will not switch back on it's own.
The plugin works in conjunction with MQ2MoveUtils to stick to the target. Depending on what stick commands you tell MQ2MoveUtils, it may follow something even if you change the targets.
Otherwise I think it may be your macro that is checking if you are on the correct target... and if not it retargets.
One way you can check this is to either "/end" the macro or use "/mqp" to pause the macro fully, then try switching targets during a fight.
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You may try asking in the KA boards about what other folks do to pause or do manual style things during operation.