Jungle leaves become see through when blocks placed on two sides and signs do not change colour when using § anymore

Hello,
When I place a see through block such as leaves on one (or two) side of jungle leaves, the block suddenly becomes transparent and turns to the sky blue colour. It only happens on 2 adjacent sides, the other two don't, and only happens with see through blocks.

Signs also don't change colour when using the § command, only turning very faintly to that colour which is barely recognizable.

Thank you.