SPIN assert not triggered - model-checking

Question

I am trying to understand why the assert in this model isn't triggered.
ltl { !A#wa U B#sb && !B#wb U A#sa }
byte p = 0
byte q = 0
int x = 0
inline signal(sem) { sem++ }
inline wait (sem) { atomic { sem > 0 ; sem-- } }
proctype A() {
x = 10*x + 1
signal(p)
sa: wait(q)
wa: x = 10*x + 2
}
proctype B() {
x = 10*x + 3
signal(q)
sb: wait(p)
wb: x = 10*x + 4
}
init {
atomic { run A(); run B() }
_nr_pr == 1
assert(x != 1324)
}
Clearly, there is an order of operations that produces the final value x = 1324:
Initially x = 0
A sets x = 10*0 + 1 = 1
B sets x = 10*1 + 3 = 13
A and B allow each other to proceed
A sets x = 10*13 + 2 = 132
B sets x = 10*132 + 4 = 1324

Answer 1

The assertion isn't triggered because it is "never reached" when the solver proves that the property
ltl { !A#wa U B#sb && !B#wb U A#sa }
is true.
Take a look at the output that is given by the solver, it clearly states that:
it is checking any assertion, but only if within the scope of the claim:
Full statespace search for:
never claim + (ltl_0)
assertion violations + (if within scope of claim)
the assertion isn't reached:
unreached in init
t.pml:27, state 5, "assert((x!=1324))"
t.pml:28, state 6, "-end-"
(2 of 6 states)
You can use the option -noclaim so to check the model only for the assertion, which is then easily proven false:
~$ spin -search -noclaim t.pml
ltl ltl_0: ((! ((A#wa))) U ((B#sb))) && ((! ((B#wb))) U ((A#sa)))
pan:1: assertion violated (x!=1324) (at depth 13)
pan: wrote t.pml.trail
(Spin Version 6.4.8 -- 2 March 2018)
Warning: Search not completed
+ Partial Order Reduction
Full statespace search for:
never claim - (not selected)
assertion violations +
cycle checks - (disabled by -DSAFETY)
invalid end states +
State-vector 36 byte, depth reached 15, errors: 1
48 states, stored
6 states, matched
54 transitions (= stored+matched)
1 atomic steps
hash conflicts: 0 (resolved)
Stats on memory usage (in Megabytes):
0.003 equivalent memory usage for states (stored*(State-vector + overhead))
0.286 actual memory usage for states
128.000 memory used for hash table (-w24)
0.534 memory used for DFS stack (-m10000)
128.730 total actual memory usage
pan: elapsed time 0 seconds