Heavy Stun Buildup on Player

Apologies if this is not a bug or is intended but it feels like it could be an issue with incoming heavy stun build up and blocking/parrying. I've recently been trying the Huntress and using the Parry skill from a Buckler. As expected, when I parry it fills the heavy stun bar for me, the player, unless the evasion kicks in and I avoid it. However I am finding that sometimes after I stop parrying, certain hits from enemies are still building up heavy stun on me. This seems more common if I was heavy stunned already and have a filled bar, where I can at times almost be chain heavy stunned by enemies. From the tooltip on stun and heavy stun, my understanding was that we should only receive heavy stun while blocking/parrying/on the Rhoa. I am just wondering if this is a bug or are some enemy attacks expected to cause heavy stun build up on us? Thanks.

EDIT - Added a bug report ID - Bug Report ID: #3171143955

Video here - https://www.reddit.com/r/PathOfExile2/comments/1nrtci7/bug_heavy_stun_continues_to_build_after_a_parry/

Just posting to say I accidentally duplicated ths issue described here that also has a video showing the issue - https://www.pathofexile.com/forum/view-thread/3830567