Problem Details: I DT FC'd https://osu.ppy.sh/b/345283?m=0 this map, and it gave me

this amount of pp, and my rank increased +1, whereas, when I DT FC'd https://osu.ppy.sh/b/245850?m=0 this map afterwards, it gave me

this amount of pp, and my rank increased about +26.
I don't get how the ppv2 system works based on that.
Please explain?? Is this some kind of a glitch?
EDIT: corrected +18 to +26
osu! version: 20140529.4 (latest)
this amount of pp, and my rank increased +1, whereas, when I DT FC'd https://osu.ppy.sh/b/245850?m=0 this map afterwards, it gave me
this amount of pp, and my rank increased about +26.
I don't get how the ppv2 system works based on that.
Please explain?? Is this some kind of a glitch?
EDIT: corrected +18 to +26
osu! version: 20140529.4 (latest)