The title might sound confusing, so in very clear steps:

- Issue right now: whenever L-clicking any unit/hero (friend or foe), your focus is shifted on that particular unit. That means your entire HUD tries to display characteristics of that unit.
- Issue followup: as soon as you clicked any other unit/hero, you cannot do anything else with your Hero until you select it again (click on it, F1 etc.).
- Sub-issue: sometimes you actually don't realize you do NOT have your Hero selected, because the entire interface is the same. Split seconds of confusion are enough to kill you. Several seconds uselessly trying to buy things at the vendor are enough to be frustrating.

- Suggestion: make a distinction between selecting and focus. Controlling your Hero would mean FOCUS, checking out on other heroes/units would mean SELECTION. You should never be able to lose focus of your Hero (with the exception of controllable units, see Minion/Illusions below).
- Sub-suggestion: build a different, smaller HUD for the target of your selection, in order to show its details. This HUD window would only stay up for as long as you have that particular unit selected.
- Minion/Illusion suggestion: these units should be subject to player focus as normal.