Some words are typed correctly but are not recognized by the system without pressing the ENTER key

When I type the correct answer it is not recognized by the system without pressing the ENTER key. This does not happen with all words even though the settings are for all words. This is confusing because it does not appear to have been answered correctly, but in fact it is

Does those words have something in parenthesis, ex moon (satellite of Earth), if so then you need to hit the Enter/Return key.

There is nothing in parenthesis. Currently, the only word is CONSTRAINT that behaves like this, but I see no difference with other words. For all other words, I don’t have to press ENTER.
For example, there are two EDITING ALTERNATIVES for the word CONSTRAINT, but this also applies to the word IMPEDIMENT, which I do not have to press ENTER.
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There seems to be a trailing whitespace which could create the problem.

It could be a difference in the register (O,C vs o,c). I’ve noticed earlier that web version is case sensitive.