To reproduce: place vector pdf as figure into a Manuscript file, then export file as pdf ==> the figure gets rasterized at a very low resolution rather than preserving vectors.
Bug: vector pdf figures get rasterized upon pdf export
Don't hold your breath. I posted this same issue last February or March and there's been ZERO action on it. Clearly, nice looking figures are not a priority for the developers.
thanks for your message. I'm also a little concerned that despite the present hiccups in Manuscripts support is somewhat inconsistent (http://support.manuscriptsapp.com/topic/584/feedback-response-to-bug-reports). However, at the same time when not encountering errors I really enjoy using Manuscript's clean layout and some of its functions, so I'm currently giving it another try and will file bug reports/feature requests in the forum. Hopefully Matias will find the time to address these in the future. I'm also wondering what the current state is in terms of the extended functions such as a commenting, text highlighting etc., but feel that there are still too many more basic features (cut and paste, preserving figure vector nature, buggy sectioning/sub-sectioning, no drag-and-drop support to name a few) that hopefully get addressed first.