I agree with PastMaster completely. Whilst you specifically may not be doing anything illegal (I do realise there are legitimate reasons to download large files), now that mIRC is such a hugely popular program the masses have to be taken into consideration.
The board policy here states that we don't help with mass/illegal file trading, many #mIRC help channels across IRC back this message up and Khaled in his personal FAQ states that he doesn't approve of the illegal uses mIRC is made to be a part of. Now that all of this is said, to then go and improve upon the ability to receive files may
seem a little odd even if the intention is to improve receiving for legitimate users.
The DCC Protocol is known to be not exactly perfect for receiving files. I've personally never had a problem with it, someone sent me 7 pictures of their house once at the same time and they all came through fine. However, some people do have issues, and often it's because their downloading huge files, often from XDCC bots or FServes, and this trend is growing. Personally, I'd rather not see mIRC contribute to this growth
And the Flush Files option that Online suggested sounds like it should, in part, help you with what you're experiencing.
My 2 cents.