When you put someone on block/ignore on client I noticed you can't check your message history with them afterwards. I'm unsure if your pm log file is erased in the PM folder but I'd figure so ;p
My suggestion is to allow you to see message history even while you have someone on block (and to not erase the pm logs file if it is erased -_-.) This is pretty handy for some situations as you may sometimes need the log of something said by someone you blocked for future reference, example; blocking someone for harrassing you through pm and wanting to show the log to an admin.
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