Under the circumstances, I believe it is caused by the use of "MultiViews"
example:
Options Indexes FollowSymLinks MultiViews
If you do not want to use it, just remove it
Options Indexes FollowSymLinks
If the "redirection" is not caused by "MultiViews", it is probably some url rewriting rule (mod_rewrite).
There are other possibilities, but I find it difficult to be out of these two hypotheses.
off:
Sorry for commenting, but I did not understand the term "defect" in the comments above.
Is this a term used in Portugal?
In online dictionaries of Portuguese from Portugal, this word has the same meaning as Brazilian Portuguese.
Anyway, the correct word would be "default."
[updating]
A more appropriate title for this topic would be "Apache interpreting a directory as a .php or .html file."