Speed buffs from different classes/jobs with the same %increase work differently

Issue:
Ley lines, blood weapon presence of mind and shifu apply differently than hutton, greased lightning and reprisal when you also have expanded arrow buff.

I have done extensive testing of the way gcds work in ffxiv and have made this calculator with the results for quickly comparing how these buffs function differently when combined with other speed buffs
https://docs.google.com/spreadsheets...it?usp=sharing

Date & Time:
4.0-4.55
I have been testing the gcd formula over this expansion to collect enough data, I have checked in game in the current patch to insure the issue still exists.

Frequency:
The issue is is repeatable with 100% success

Class/Level:
I have done the majority of my testing on level 70 jobs, though my small sample of lower level tests have show the same issue is present.

Party or Solo:
The issue can occur whether solo, or in a party, but it is easier to replicate in a party

Area
I performed tests in multiple places to get a large sample of speed buffs, but most of the tests were performed in a housing ward unless I was getting a buff from mobs only available in an instance.

Steps to replicate
1)Have a blm,nin and ast in a party
2) make sure the blm and nin have no spell/skill speed on there gear
3) have the ast draw cards till they have an expanded arrow ready to use
4) have the blm and nin get the ley lines/ hutton buff
5) have the ast use expanded arrow
6) look at the GCD for the blm and the nin, they will be different despite them both having a 15% and a 5% speed buff and the same spell/skill speed.

If more exact examples are needed I can come up with more but there are to many to list them all in this report.