I just checked BOM on Mouser and Digikey. Both sites flagged IR4428 as obsolete!Hi EG,
No that pin arrangement is intended.
Discharge gives a nice fast clean drive for the gate driver chip and the CMOS 555 Q output swings rail to rail so it generates accurate timing.
Good observation though.
PS latest schematic at post #38
Also 47uF tantalum there is a major cost difference between 5% and 10% tolerance ($2.50 vs $15.50). These things are not cheap.