Hi
Happy to see that you consider the "hole" as strange behaviour.
Some answers to your question :
these allocations are very complex, are they really needed to be so complex (several allocations to project...)
As you know, there are many steps during software lifecycle. For example, a project manager will work more during build steps and less during run step. In fact, if I could (If I had enough time to do it), allocations would be more complex because during build step a project manager will work more during specification and test steps and less during development step. That's why you can see several allocations to project. It's the way I found to be near reality.
you don't need to allocate resource to "Absence" if it is an "administrative" project
If I don't allocate resource to "Absence", I won't be able to plan holidays (In France, you have to take rest to respect the law

). In a year, there are 365 days minus 104 days for week end minus 7 days for public holidays. It lets 254 days for working days. In my company, a resource can take until 42 days for vacation by year (25 days for holidays and 17 days for RTT). 42 days divided by 254 days is near 16% of working days ... If I don't "lock" this vacation time with allocation to "administrative project", I could believe that a resource is available more than 100% by year. Later, I will divide year with 2 periods : June to October (In France, Act imposes that a resource takes 20 days for holidays during this period else you have to give until 2 days more for the fractionning of vacation ... Dura Lex Sed Lex) and November to May for the remaining part. But I will wait that you solve my "hole" problem
Regards