What version of Thunderbird are you using?

Thunderbird 45.1.1 I would have got this back to you sooner but you replied to me via the no-reply email! Anyway thank for prompt attention, see if you can throw some light on this niggle. ALAN

That is because you reply in this forum. There is no need for email.

Do you paste the text into Thunderbird from somewhere else? The only way I can see this happening is if the word is in two parts in the underlying HTML codes

This is possible, but usually requires reformatting only part of a word or pasting from something like Word.

Try restarting Thunderbird from the help menu with add-ons disabled. I think that had best be the starting point here.

Not pasting in text from anywhere. I am typing very simple text (words). I have tried now in safe mode and after a couple lines we had the same issue, several letters at the start of a word were ignored as regards the spell checker, hence half a word is 'misspelt' corrected it, several words later exactly the same error reappears, again we correct it, again it errors (same letters missed hence a misspelt word. Over to you, thanks Alan

can you send me an email that demonstrates this (do not correct the incorrect spelling) Save the email as a file before sending and attach that file to another email and send to unicorn dot consulting at gmail dot com

I will have a look at the structure and see what if anything I can see that might be the cause.

Do you move around in the mail with the mouse (move insertion points) or use the back space key a lot?

Thanks for prompt reply, last question first. I move around in the email with equal proportion ie mouse and back space. I have tried to analyse that function, nothing specific. I do not know if the misspell underline transmits, not checked with any recipient. I will send a demonstration when one occurs, ie it doesn't occur every email but some times several times in the same email. My test yesterday had the problem repeated 3 times in the same place. half the word was ignored-I corrected it several words later the same 'error' appeared- correct. several words later reappeared, very strange. ALAN

Further-I 'copied' an error as described, when it transferred to another email prior to sending the red underline disappeared. Another 'error' transferred to a sending email for you did have the 'error' on board till I used the space key-error disappeared. I then copied a REAL error onto this other email, that stayed..........ie it is an error in both emails. Alan

Re above, I have tried several times 'capturing' the misspelt word but bearing in mind that it is not a true misspelling as it is transfers to another email it often 'disappears'. A real misspelt word can be transferred. Even just using 'copy' to eventually 'paste., often clears the problem. It only happens about once or twice ever other email. But can reappear in the same place after clearing. Over to you. ALAN

I have worked out what is happening.... just not why it is happening.

Thunderbird is putting a HTML font tag in the middle of the words. But I have so far only seen it once and have not been able to reproduce it consistently. When I can I will file a bug. Or you can. https://bugzilla.mozilla.org/

M Thanks for above thoughts on the problem. Can I ask you to file the 'bug' as I haven't an account nor am I sure on what I should be putting on the page. The problem seems to have reduced of late but can still appear and repeat in the same place. Alan O