I CANNOT MERGE TWO LAYERS CONTAINING TEXT IN 3D SPACE

Hello everyone, 

One text layer in 3D space: Hello

Another one text layer in 3D space: World

When I select both of them and go to 3D > Merge two layers (or ctlr + E), the following appears. I am not sure where the text goes, sometimes the black at the back flies on the top right. Please do you have any recommendations? Many thanks.

1st picture: both layers are seperated:

2nd image: result of merging the two 3D text layers