Special characters not rendered properly

Hello,

I have a small problem with a couple of Helvetica font assets which are mis-behaving, and i don´t actually know if i´m doing something wrong on my side or not.

One font is a the HelveticaNeueLTBd, which is a bold simulation, the other one is a the normal HelveticaLtProRoman. It looks like when it comes to specific characters like ü ö ä and so on, the "bold" one actually comes out normal on some of this characters, while the normal one actually renders bold these.

I thought it was because of some wrong fonts i downloaded, but it happens also with some specific provided fonts used on the web and correctly behaving, so there must be something i´m missing from my side.

Thanks a lot in advance.