and as it turned out in truncated form:
Note, that the two last dots are gone, and if the address is clicked on at YouTube comments, the browser is taken to a "404/Not found" page in Memory Alpha.
The article about what Star Trek is, actually does contain three dots at the end of its address, but the YouTube comments system doesn't like it, as I found this out through my Google+ notifications on the desktop and the (linked) comments at desktop YouTube.
The somewhat unorthodox solution to avoiding dots from being truncated is to insert the URL with those three ending dots and replace the two last-most dots with their percent-encoded representations. Case in point:
That one dot there may remain.
The percent-encoded values are available from Windows Character Map, a similar program in UNIX/Linux, or through any Unicode character table available on the web.
One can also try with
— with "typed dot | precent-encoded dot | typed dot" after "_is", but there cannot be any two or more concurrent normally-typed dots.
Truncation of characters in addresses pasted (or typed) into YouTube comments can also apply to other web addresses with multiple concurrent characters, but I do not know, which types of characters are more affected or less. I could lay a claim, that special and non-alphanumeric characters that are used in programming, are treated with a greater level of scrutiny.