I'm getting this error from the pool (when using the new "-pow7 1" in v4.0):

04/04/18-15:09:15 - SHARE FOUND (target 35000) - (THR 3 of 10)
Share rejected (47 ms)!
{"id":4,"jsonrpc":"2.0","error":{"code":-1,"message":"Lowdifficultyshare"}}
04/04/18-15:09:29 - New job received from pool.minexmr.com:7777
Speed: 341 h/s, TotalHashes: 10K, Mining time: 00:00
04/04/18-15:09:58 - SHARE FOUND (target 35000) - (THR 9 of 10)
Share rejected (62 ms)!
{"id":4,"jsonrpc":"2.0","error":{"code":-1,"message":"Lowdifficultyshare"}}
04/04/18-15:11:09 - SHARE FOUND (target 35000) - (THR 5 of 10)
Share rejected (47 ms)!
{"id":4,"jsonrpc":"2.0","error":{"code":-1,"message":"Lowdifficultyshare"}}
04/04/18-15:12:53 - New job received from pool.minexmr.com:7777
Speed: 315 h/s, TotalHashes: 80K, Mining time: 00:03
04/04/18-15:12:59 - SHARE FOUND (target 35000) - (THR 4 of 10)
Share rejected (47 ms)!
{"id":4,"jsonrpc":"2.0","error":{"code":-1,"message":"Lowdifficultyshare"}}

- What's the problem?

- It's all ok if I don't use the -pow7.
(The pool says "Switch to new PoW now! - Before April 6:th")
EDIT: I'm using minexmr.com on port 7777.