Luminous particle shield can block ion, but has -100 malus to resist. A continuousBeam weapon with ion:7d4; shield:7; WMD:3 hits Luminous with the particle shield. The beam does no damage to shields. I switch to a weaker ion beamer with no shield buster, and the shield quickly evaporates (because the shield is optimized to block particle damage, not ion). Curiously, I tried the Dvalin Ion9, which is a particles style attack with shield:9, and it made short work of the shield too.

UPDATE: After more experimentation, it turns out that high shield buster level, possibly combined with high weapon damage, makes the Luminous particle shield immune to ion damage. Then I lowered shield buster to 1, tried it, then removed it, and both times it could damage Luminous particle shields, but then it got resisted by Luminous ion shields (as expected).

I do not know what is causing this anomaly. It seems like a rollover bug or something similar.