Error concerning calc() while validating file

Dear Madame, Dear Sirs,

My description:

The file attached (gk1.css), a simple css-file, receives the error in 
line 117:

Ungültige Nummer : width Einlese-Fehler :calc(100% - 215px)

(My translation: invalid number : width read-error :calc(100% - 215px))

As far as I found information in the archive/report this seems to be a 
bug in the validator (but the date 2015 seems to me a bit too old be be 
true).

If you see the link

https://www.w3.org/TR/css3-values/

and there:

Example 14

I'm sure, that this is no error in the css-file.
The site I'm building looks fine and seems to work in a proper way, with 
a correct calculation of the sizes, when using gk1.css.

I'm using Opera 36.0.2130.32, Update-Stream:Stable, Windows 7 64-bit 
(WoW64).

I thought this is worth to open an issue, despite the validator is a 
nice pice of software!

Kind regards

Supporter of www.g-kauft.de