What we observe is this behaviour

• PR created.
• Comment (runbuild) added to PR and that triggers the build
• Build fails (for whatever reason)
• Developer pushes more commits into PR branch a few days later
• stash plugin triggers the build immediately. Comment was NOT updated with runbuild keyword

This appears to be a bug, because, Plugin seems to get confused (or it is intentional?)
It should not trigger builds on new commits, only on keyword in PR comment.