Resources links appear as if they're "cached". Here's how to reproduce, I'll let you qualify the actual issue (i'll also let you fix the lousy wording below):

• add a resource-ref in your site's scriptloader "chain", such that a given library is loaded on each page.
• modify the library in question.
• changes don't seem reflected.

I suspect it might be only the case when resource-refs are aggregated, but haven't investigated further.

I'm not sure which version(s) are affected, but I think 2.5 and 2.6 ? Happened on 5.1-snapshot yesterday.