I must have had a target on my back today!

In screenshot 1, you can see that the "close italics" tag isn't recognized, and in shots 2 and 3, you can see that adding a preceding instance results in the recognition of subsequent instances.

In shot 4, you can see that the "strikethrough" tags don't affect the entire text around which they're wrapped, and in shot 5, you can see a second example of the same, as well as some really weird behavior as respects joemikeb's post and my quote of it.

This sort of erratic behavior isn't terribly common, but why does it happen at all?

The issues all stem from an open [i] tag in joemikeb's post. Since the original closing [/i] tag was mistyped, that opening tag had no effect in his post; but when the quote was incorporated into your post, a closing [/i] tag was found. (See violet circles.)

Yes, you would expect the displayed italics to carry on beyond the quoted snippet, but predicting the specifics of how mangled tags will florf the displayed content has always been well nigh impossible, probably due to the way that the UBB software (or the browser interpreting the HTML code it converts UBB code into) tries to correct the improperly implemented tags.

For instance, in your first screenshot, as further marked up by me, a reasonable inference is that since tags must be nested, but the [quote][/quote] tags and the de facto [i][/i] tags overlap, UBB or browser software attempts to correct this by interpreting the closing [/i] tag as occurring inside of the closing [/quote] tag.

Further analysis is left as an exercise for the reader.

Florf ? Can we assume that someone, like many of us, spent a lot of time with Don Martin cartoons?

I don't think so. Don Martin used a sketch pad (not a computer).

This takes us back 3 years to artie's question What's happening here?
where "florfed" was used as a past participle qua adjective meaning completely ruined, inactivated, disabled, or destroyed; especially when used in reference to computer software or electronic gadgetry.

Now it would seem to have morphed into a standalone verb (and will probably show up as a noun sometime soon).

When I suggest a computer user has employed a Don Martin-ish type word, it doesn't mean I thought Don Martin used a computer.

Anyway, no one chuckled and the moment has passed.

True dat. And I did chuckle; I even chortled.

The second I saw "The issues all stem from an open [i] tag in joemikeb's post." I immediately realized what had happened.

I've seen the results of incorrect closing tags many times, but this is the first time the italics didn't continue all the way to the correct tag, and that, combined with the fact that I just plain missed the extra italics in the quote, left me at a loss.

Thanks for kicking in.

But what about the florfed spawn of the "Strikethrough" tags?

Edit: If "Further analysis is left as an exercise for the reader." suggests that I can figure it out myself, well...it's not a very good suggestion.

If "florf" was a Don Martin word, I can't find a single reference to it. (A website that sounded like it hosted a DM dictionary closed down, literally, yesterday...exceptionally poor and inconsiderate timing. )

I dunno... I can't think of a single context in which Martin may have used the word; have you got an example?

I gotta chime in in support of ryck who only suggested that "florf" is "Don Martin-ish type word" — which indeed it, like many others (from memory), is.
As an aside, I suspect his neologisms were directly related to his inimitable cartoon style.

It's not a suggestion. It's a declaration. If, despite my statement that "predicting the specifics of how mangled tags will florf the displayed content has always been well nigh impossible," you still want logical explanations for the other anomalies you observed, you're on your own. I haven't got the time.

OK, I'll buy that. I took ryck literally, as I'm prone to do.

No need to get huffy!

""Further analysis is left as an exercise for the reader"" suggests that you saw something that I missed and that further analysis would be fruitful, rather than virtually useless, as you're now saying you might have simply said from the get-go...

Okay by me. Sklork!!