"make installer_sis" will always recreate sis file for projects that have path in TARGET (e.g. TARGET = ../foobar), because the sis will actually be always created in the same directory as .pro, so dependency $$(TARGET) is always missing. Since typically you want to have properly signed sis to use with installer_sis target, it is very undesirable to have it get overwritten.

"make deploy" doesn't work either because of the same root cause, as it attempts to install sis from incorrect directory.