Bzuco,
actually you have to look at initial Tie Points detected in both runs which is very similar :
132,728 of 387,261 for version 1.7.3 and 119,143 of 388,119 for version 1.7.4.
The final tie pts number (132,728 vs 119,143) depends on the gradual selection done in each case which was tighter for 1.7.3.
PS. if you still have the installer for 1.7.3 on your system, just disinstall 1.7.4, re install 1.7.3 and move it to a different folder. Then re install 1.7.4 again to default folder... You will now have 1.7.4 in default folde and 1.7.3 in a different user defined folder...