I am able to save my project (Save Project As...) to a directory with a ; in the name (e.g., "c:/test;area"). There is no warning or error indicating that this is not valid. However, when there is a ; (semicolon) in the name of the project directory, Synthesis does nothing when running in the GUI, but it looks like it finishes. When you Run Implementation, it says there is no synthesized design.
To avoid this issue, do not use semicolon in a file/path name.
Alternatively, you could run Synthesis with the "synth_design" tcl command using a non-project flow.