When using indents for the Code Block macro, it can display different behaviours, depending on the "combination" used. With the screenshots below, we can get a better picture of it:

Using the left indent, in the first line and two for the second, before saving and the result:

Result:

By using the same level of indent for two lines:

Result:

And finally, if you do not use the indent in one of the lines, it will behave as expected:

Result:

This seems to be a regression from this other report, which we have fixed for pas versions of Confluence.