I think that you will find that the practice was not that uncommon on the older 90kts S & L seats where ejection was not an option at taxy speeds. After an hour plus of being tightly strapped in to a seat that had no compromises to comfort, it was often a merciful release to be able to restore feeling to one's nether regions. Loosening off shoulder straps just didn't do it. So, on clearing the R/W it was pins in often followed by various levels of unstrap