Perfect Timing not reducing cooldown of Guardian Angel

Server: NA

Type of Bug: in game

Description: Perfect Timing rune not actually reducing cooldown of Guardian Angel like it should. Timer is reduced to 255 seconds but the white symbol does not appear on the champion and the revive is not in effect until the full 300 second cooldown passes

Steps to reproduce: Buy GA Die After 4 minutes and 15 seconds the item appears to be off cooldown in item bar. die again before 5 minutes pass do not get revived

Expected result: cooldown of GA is reduced by rune

Observed result: cooldown of GA APPEARS to be reduced but is not

Reproduction rate: 100%