Input.Mode max 8?

I try to use a mask over 8, but it always shows this:

Input.Mode .....: Mask (?1?1?1?1?1?1?1?1) [8]

I've tried 10, 12, 15.. it always indicates 8 instead, is this the max supported mask when brute forcing?

I'm using cudaHashcat64.exe with a GTX 970.