The problem isn't mouseovers but heals.

It's okay to use multiple targets in macros for non-heal non-selfbuff actions.

For example, in a ground target macro, it's okay to do this:
Code:
/ac Asylum <mo>
/ac Asylum <t>
/ac Asylum
/micon Asylum
This will center Asylum on mouseover if available, then on target if you have a target, then give you a cursor for manual placement if you have neither a mouseover nor a target.

This works because if you have no mouseover, the first line is invalid, so it skips to the second line. If you have no target, the second line is invalid and it continues to the next line. The third line gives you a manual ground target cursor.

However, you cannot do this with heals and self-buffs because heals and self-buffs are programmed to coerce a self-target if <t> is invalid. If you try to heal mo>t>me, if you have no mouseover the <mo> line will be invalid and it'll skip to the <t> line. But at the <t> line, if you have no target -or- your target is invalid, the <t> line will cast on self. The <me> line is moot.

If you want to use mouseovers for healing, you can (I do), but whenever you have an action that can coerce a self-target when <t> is invalid, you should only have a single action in the macro, on <mo>.