Tigra R3 glitch?

I just took my r2 duped Tigra (14,200 pi at r2) to R3 and her pi went to 13,800 upon ranking her up. Currently I have her at level 20 of R3 and she just got back to the 14.2 pi. I have NEVER noticed this happen on any rank up in my 6-7 years playing. Am I oblivious and this is normal or is this a glitch of some sort.....I know PI isn't the end all be all and I'm not in an alliance where I really care about prestige but what is going on? Has this happened to anyone else when ranking up a champion. Fwiw, this is like my 7th or 8th R3 and the first time I've noticed this happen
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