Problem:    Mouse test fails on MS-Windows.
Solution:   Set 'mousemodel' to "extend".

Problem:    Spell test fails because of new illegal byte check.
Solution:   Remove the test.

Problem:    Can add invalid bytes with :spellgood.
Solution:   Check for a valid word string.

Problem:    Conceal character from matchadd() displayed too many times.
Solution:   Check the syntax flag. (closes #10381, closes #7268)

Problem:    Fuzzy expansion of option names is not right.
Solution:   Pass the fuzzy flag down the call chain. (Christian Brabandt,
            closes #10380, closes #10318)

Problem:    Mouse in Insert mode test fails.
Solution:   Fix the text and check relevant positions.

Problem:    String interpolation in :def function may fail.
Solution:   Do not terminate the expression. (closes #10377)

Problem:    Popup_hide() does not always have effect.
Solution:   Add the POPF_HIDDEN_FORCE flag. (closes #10376)

Problem:    Using execute() to define a lambda doesn't work. (Ernie Rael)
Solution:   Put the getline function in evalarg. (closes #10375)

Problem:    No text formatting for // comment after a statement.
Solution:   format a comment when the 'c' flag is in 'formatoptions'.