cmake incorrectly converting double slash to single slash

Been using cmake 3.5.1 for ages and looking to update to 3.14. One of my projects fetches a private git repo via ssh using the external project command with something like:

ExternalProject_Add(
 my_external_lib
GIT_REPOSITORY ssh://user@myserver:/path/repo.git
... # //other stuff
)

In cmake 3.5.1 this worked fine, however in 3.14 the double slash is getting converted to a single slash and causes retrieval to fail (with error cannot resolve ssh:/user@myserver:/path/repo.git) It doesn't make a difference if I enclose the path in double quotes.

ccmake does something similar--if go into ccmake to edit the path and re-add the slash, ccmake immediately removes it when I hit enter. If in ccmake I edit the path to have a triple slash (ssh:///user...) then when hitting enter it changes it to the expected double slash. I am using Ubuntu 16.04.