Using Tbird 32 bit 52.1.1 Windows 10. Spellcheck is on so it redlines words I misspell. Often I have misspelt a word, the correct spelling of which I have added to my personal dictionary. I right click on the misspelt word to select alternatives. The spellchecker never suggests one of these added personal dictionary words, only words from the main dictionary. When I manually correct the misspelt word to the correct spelling, the redline goes away, confirming that it 'knows' the word.

I attach jpegs with snips showing a spellcheck highlighting correctly marked right and wrong spellings of 'lorikeets' and the section of the personal dictionary showing the added word 'lorikeets', and a screen shot showing that the spellchecker does not suggest 'lorikeets' from the personal dictionary but a very different word ('strikeout') from the main dictionary.