I have noticed a bug in the import workflow tool. When you import one archive (haven't tested a unzipped workflow) everything goes well, but if you try to import another archive, the button is not responding. The only solution is to quit KNIME and then KNIME crashes when quitting. I have seen that everytime I did it. I'm using 2.11.3 on several Mac.
I have reproduced this behaviour on 2 Macs, both using Yosimite (curse Mac!). The bug happens when importing an archive. In all cases, after import I opened the workflow before attemtping to import a further one. When I import another one, the "browse" buttton is unresponsive.