I'm doing a quick comparison of tags for Eldritch Blast and Rapier. Can't seem to find anything that would indicate a reason why it is unselectable as a weapon. The reason given when hovering over the non-selectable symbol says I'm not the right size. Oh well I was hoping to assist with fixing this bug.
Yea, this is actually intentional. I can probably make it selectable, but I didn't see a reason for doing that since you can't really "wield" it. I suppose since you can't use it while holding a weapon, it could be useful?
Unfortunately I did find a bug too. I'm making a new version of my Rogue/Warlock and tried to pick the Thay trait. As a result I also picked the Mind Over Body free feat. It gave me the feat but shows that I do not meet the requirements of race. It is also not using the ability that I selected for my HP modifier. I tried both and neither work. Is this because I don't meet the requirements?
What is your race? The eval scripts on the trait and feat both appear to be looking at your race. The hp bonus appears to be tied to how many Metamagic feats you have. Do you have any?