other spells ive seen this happen with are frost giant and rebirth. i think for rebirth specifically, this glitch started happening after the spell had its ending removed in the AoE update, making revamped bartleby instantly vanish once players get healed. while updated rebirth looks very pretty now, the animation itself is somewhat of a downgrade (more awkward & sluggish than before), in addition to the glitch dayerider described, which happens often. frost giant and storm lord did get similar treatment to rebirth, where their stun animations were removed after the AoE changes, so maybe thats why this glitch happens to them too?
hope this info helps. thank you for bringing this issue up