Liu (2004) criticized the black hole coalescence model on the grounds that
calculations based on general relativity show that the change in inclination of a rotating central SMBH is negligible in a minor merger and a significant reorientation of the active SMBH requires a comparatively rare major merger (Hughes & Blandford 2003).
This erroneous statement probably had its origin in the final sentence of the Hughes & Blandford paper, which states that
An abrupt change in inclination […] requires a comparatively rare major merger.
Hughes & Blandford defined a “major merger” as having a mass ratio q > 0.1, in conflict with the standard definition among galactic dynamicists, q > 0.3. In fact Hughes & Blandford conclude, in agreement with Merritt & Ekers (2002), that mass ratios exceeding ~ 0.2 can result in spin-flips.