Some ingame graphics, such as AG256 (Used by the M2, M5 and ThermoExplosion effects) and rsArmorhit1, are built using Luminous to make a nice rounded or otherwise not-square edge. However, the way that they've been output from Luminous has truncated the effect, resulting in straight lines appearing towards the end of the effect. It'd be nice if these could be re-rendered at some point in future so that they look as awesome as they would in Luminous. They're great effects...but we're not seeing the full effect. I'm not sure of the exact number of affected effects, but there's probably a few more besides those two.
Technically this is a graphical bug, but it's so minor that I'm putting this as a suggestion rather than a report. It's not strictly necessary, but it'd make things look an awful lot better.