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It's because the price of STEEM is going down (or was... its about the same since few days). I saw the post money going up (without extra votes) when the price was rising. It works both ways.
You can see it Account value too. It all changes with the change of Steem - goes down or up.

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STEEM 0.16
TRX 0.13
JST 0.027
BTC 57560.27
ETH 2570.10
USDT 1.00
SBD 2.48