Current behavior:

• no combat + no mouseover -> hidden
• no combat + enter mouseover -> shown
• no combat + stay mouseover for some seconds -> shown
• no combat + stop mouseover -> hidden
• combat + no mouseover -> hidden
• combat + enter mouseover -> shown
• combat + stay mouseover for some seconds -> hidden (!)
• combat + stop mouseover -> hidden
• mouseover + enter combat -> hidden (!)
• mouseover + exit combat -> hidden (!)

Expected behavior:

• no combat + no mouseover -> hidden
• no combat + enter mouseover -> shown
• no combat + stay mouseover for some seconds -> shown
• no combat + stop mouseover -> hidden
• combat + no mouseover -> hidden
• combat + enter mouseover -> shown
• combat + stay mouseover for some seconds -> shown (!)
• combat + stop mouseover -> hidden
• mouseover + enter combat -> shown (!)
• mouseover + exit combat -> shown (!)

It's a round about way of saying that I'd expect bars to show on mouseover and hide on no mouseover regardless of any other condition (combat state or whatever else).

When does it fade out

• Are still in combat?
  Yes

• after a set amount of time after mouseover?
  No there is no set amount of time. Sometimes it about 1s, sometimes its less.

• After leaving combat?
  Yes, when mousing over (bar shows) and then entering combat, the bar hides even though I'm still mousing over.
  The same is true for leaving combat: When mousing over (bar shows) and then I leave combat, the bar hides, even though I'm still mousing over. This one is a bit tricky to even do though, because during combat the bar keeps hiding shortly after mousing over.