Internal MBP monitor disabled after opening lid
When using certain applications (namely, any Native Instruments product, e.g. Kontakt and Creator Tools), DisplayLink behaves strangely as reported in another issue.
I'm used to keep the lid closed in order to use the external monitor only. Under certain circumstances, reopening the lid will keep the internal monitor disabled (i.e. black screen). The only workaround for this is hard-reboot.