I encountered this bug recently when a wither skeleton killed me while I had the Fire Resistance effect.
-keepInventory was on
-I had a Fire Resistance potion effect
-A mob killed me (using the Wither potion effect)
-When I respawned, I, as expected, did not have either potion effect anymore; BUT the particle effects from the first potion effect were continuing (even though I no longer had the effect).
Yes, confirmed in 21w03a.