Words ending in '-el' are an exception to the general rule in BrE.
rivalled/rivaled - doesn't end in -el. Nor does devilled, which I've already given.
http://grammarist.com/spelling/rival
When I tried to find 'riveted', eight dictionaries were listed. None appeared for 'rivetted'. The score in the 'fidgeted' vs 'fidgetted' match was 13:2.
So, 2 out of 15 uses of fidgetted/fidgeted used a double t. I would be more impressed with your argument if it were 0 out of 15.
Incidentally, the forms with two
ts are marked as incorrect as I type this.
I've already given
https://en.wiktionary.org/wiki/rivetted
I'll add
"verb (used with object), riveted, riveting or (especially British) rivetted, rivetting."
http://www.dictionary.com/browse/rivetting
I don't want to argue about this; it's not worth it. I was only giving information. I was not arguing that
the correct spelling used the double letters, only that in many cases, the doubled letters are still considered valid spellings.
So, I'll retract the assertion that BrE uses the doubled letters, and instead will assert that there are legitimate minority spellings (of this sort) that are used less often in AmE.
About the red lines under words, that would be a function of the word list that this editor uses. I get red lines under all the "our" words, such as honour, favour, humour. You're not going to tell me that this means they are spelled/spelt wrongly, are you? (Red line under 'spelt' as well, despite it being accepted by Oxford Dictionary).