Why does Qsys freeze and generate an empty .qsys file when saving the Qsys system?

Description

Due to a problem in the Quartus II software versions 12.1 and earlier, Qsys may freeze and generate an empty .qsys file when saving your Qsys system. This problem can occur when your path includes square brackets, "[" or "]".

Resolution

To work around this problem, make sure your path does not include square brackets.