AA Imbues - unintended exploit? : DDO Submissions

When my Arcane Archer beats the training dummy aboard guild ship, I habitually set Imbue Flaming arrows. When I go into quest afterward, most of the time I pick a different Imbue (usually Fearsome). Over last couple weeks I noticed that sometimes Imbue Flaming remains -- in addition to Fearsome or whatever. And not just the icon -- I see flaming damage numbers (and at least once flaming HEAL numbers, as I was shooting at a fire elemental). But it is not consistent. Sometimes Imbue Flaming remains, sometimes not. Has anyone else seen it, and has an idea how to control it?