We will more likely attempt to determine the source of the issue because the symptom mentioned above is most likely the manifestation of some other bug at a higher level of abstraction than the implementation of the note itself. However, some brief tests have led me to conclude that vouchers themselves are working properly.
Fixes that utilize external routes tend to spawn other issues and are to be considered bad practice, especially when there are other plugins that could cancel the intended actions of the external route. Both the current implementation and your suggestion work as intended--that is, they both either give the effect or give an item that bestows the effect. However, there seems to be an external factor independent of the voucher plugin that cancels the effect after a short period of time (approximately one second).
That being said, thank you for reporting this bug! I'm marking this particular issue as "pending."
