Hi Stefan and Pierre,
I have updated my local instance of Studio to 1.0 on Linux (as built by the 1.0 release tag) and found this potential bug. I deleted my previous ~/.ApacheDirectoryStudio directory so that there were no conflicts and started from scratch so I am pretty sure it is an actual issue.
There is an easy workaround which is to disable the "Get Base DNs from root DSE" and set up the network tab, but the fist impression is confusing. Also, as mentioned in the issue, it does not appear to happen on Windows, so I am not sure what is going on.