HRM-PRO Plus strap comes unhooked

Hello.

I've had this happen on a few occasions - where the strap comes "unhooked" from the rather rudimentary clasp. I am not sure why it has such a small "hook" at the bottom . If one has to reseat the strap whilst running , it seems quite easy for the "hook" to come dislodged and the strap come off. This has happened three times to me doing recent events. I am going to resort to securing it across the hook with run bib tape for races so as to reduce this risk. 

Does anyone else experience this? I dont think I am wearing it either too loose or too tight , Ive been using HRM's for years.