This happens on all scales in the papers. Very often I have to re-write several example paragraphs and then have the student go through the paper paragraph by paragraph and try to get each one to follow a logical progression. Abstract, Introduction, Objective, Procedure, Results, Discussion, Conclusions, References, Appendix. Often there is no introduction so the reader is left wondering what the paper is about. Very often students have difficulty in separating the important points from trivial or side issues.
Students also have difficulty with agreement in tenses and related areas.
While that is something I expect from foreign students, it is not something that should occur with native English speakers. There are proposals, papers, and progress reports, and one lives or dies by how well these are written. Aside from the plagiarism involved, such an approach shows a lack of understanding of the writing process. One's ideas should evolve while the paper is being written. Indeed, few students view writing as a tool which can aid the thought process.