I am on a physics course. Often I struggle with following mathematical derivations, so I aim to scrutinize them very carefully to make sure I understand them. Sometimes I find mistakes in the lecture notes, which are harmless from the overall point of view (ie we get the same result, it won't affect subsequent lines). Nevertheless, they are wrong. Ie instead of writing J(x) (J as a function of x), lecture notes contain Jx, ie function of J times x. We mean the former, and later use the former interpretation. Or: writing exp(0-), where 0- is the limit of x as x approaches 0 from below, while the right thing which follows from the previous lines would be exp(-0-). Of course these are equal so not much harm done, but it is still wrong. Or when on the lecture it is said that "do check this at home you will get X", and I go home and check it and the answer is not X, that seems to be problematic. Almost noone bothers to check though, so it doesn't seem to be a big issue.
My usual reaction to this is to write a kind email to the professor to point these out. I thought it is useful for both of us, he gets to correct a typo, or I get to learn something new in case it is not a typo & I am wrong. I noticed though that this is not something common to do. Once I checked this on a course, and more than half of the entries on the list of erratum in lecture notes are the things I have pointed out. Am I a weirdo and I should stop pointing these out, or this is normal behaviour?