0.17.4 save non-infinite mining productivity 15/15 level (30%) :?: sucesfully :?: converted to 2/3 (20%) in 0.17.6.

I tried again, the result:

save 0.17.4
mining productivity 30%
15 lvl (last non-infinite) done in technology tree, next infinity levels

loaded in 0.17.5
mining productivity 70%
7 ...

0.17.4 save non-infinite mining productivity 15/15 level (30%) sucesfully converted to 2/3 (20%) in 0.17.6.