There was some discussion on the front page
of similar problems, the week before last. Thanks for bringing that discussion over here; better than hijacking a thread!
I noticed that the "Quote" button disappeared a couple weeks ago, so I think that Jonathan and/or his admin person are tweaking things. In fact, I now see that the quoted text you mention seems to be gone from the composition window. (It used to appear as a partial quote, first 20 words or so, in italics and slightly grayed-out chars, and it wasn't actually quoted in the reply, it was just displayed in the composition box.)
Clicking "Reply" seems to reload the whole page, and BikePortland page loads are quite slow for me in general, from a few seconds up to 30 seconds or so, at times. I think that's a big part of the matter, the server just isn't responding super-fast, and/or is delivering a big chunk of data. (Maybe more caching would help.) It's also possible there are some security configurations on the server which slow things down (security is good but sometimes slow/painful).
For several months, up to last week, I was seeing comments hang after I clicked "Post your comment." Sometimes the page reload would never complete, but if I forced a page reload, or opened another tab so I didn't risk losing my comments, I would find that my comment had already posted. It was as if the server was not sending a "finished" ack. That might be fixed, I'm not sure.
Also, as El Biciclero pointed out in that thread, the three dots in the bottom right of the composition window allow it to be dragged to a bigger size, so you can see your reply. "...just be careful you don't drag the right edge of it outside the larger comment area or the dots get clipped and you can't drag it back again. If that happens, the right edge of your text will be hidden as well."
I see the same things with FF on Mac, FF on Win, and IE on Win (all current). q`Tzal noted some wierd quirks with a mobile browser (Android?). I see slow loads even from text browsers and HTTP tools at other locations, too.
For the "hit [Reply] twice" thing, I suspect that the composition box will eventually open up if you wait long enough (minutes?), or it might time out if the server is too swamped with requests.
Just FYI from a Van, WA, Comcast line:
--- bikeportland.org ping statistics ---
12 packets transmitted, 12 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 61.293/62.917/66.660/1.368 ms
ping statistics ---
14 packets transmitted, 14 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 64.148/70.002/79.615/5.137 ms
So, very similar ping times, yet Streetsblog loads much faster for me. I suspect the difference is the servers. I know that servers get pricey, especially as they get into high-performance levels, so I don't mean this as a complaint, just as info.