mkdir in SFTP tries to create a directory even though it exists because the SFTP client gets no information about whether the directory exists.
For a path like /a/b/c it asks at first for the attributes (isDirectory) of /a then of /a/b and so on.
This is the wrong order. Based on the permissions settings it is possible that the attributes of /a are not readable. Then it seems that /a is not a directory and the mkdir command fails.
Solution
JADE should ask at first the attributes in the reverse order, i.e. /a/b/c, then /a/b and so on until a subpath is a directory.
Then JADE should create the directories in the original order, i.e. /a, /a/b, /a/b/c