Disagree. Tax changes do not automatically require a ticket re-issue. In fact, it is quite feasible that the change in taxes in this case would be so minor that the CSA may not bother doing a re-calculation. Plus, deleting the CMB - MLE leg may actually reduce the taxes a little. Both the DOH - CMB and DOH to MLE are 4hr 55min long and both are QR flights so I'd guess that the taxes are very similar.
Regarding ticketing, an amendment to the ticket does not always require the issuing of a new e-ticket number, which is the critical point referenced in this case. When problems arise it's usually because of a change in the e-ticket number. I've quite often made minor changes to OWA itineraries which have just been amended but have kept the original e-ticket number.