Undetectable in stealth, ask yourself two questions
1: does the skill mean untrackable, or unspottable?
2: Does it apply if the track is placed on you before you disappear? Ok bear with me, what if the freep opened its tracker on you and kept the window open. You then hisped, but it then selected you from the list and tracked you. Maybe the same applies to burgs. The hips effect did not appy as the track was on you before you disappeared.
Ok I havn't answered your question just amused myself. For the record hips in the absence of sprint is not much of an escape skill, use it offensively.
"Romper: You have the power to make EM less boring for yourself and everyone else. "
"Look for your lore. But do not trust to lore, it has forsaken these lands." - Eolore prince of Lorehan