Lots of B. Indo are derived from other language, including B. Malay, grammars are mostly alike and so is the literature, but the accent differs greatly as well as some of the meanings and vocabs. We still use subtitles here in Indonesia if we watch movies in Malayu. The language are two are very different language. Even though in some terms, if both of the language are spoken by two speakers. By their own language, both are likely to understand each other, but won't be able to reply in the other's language.

Bahasa Indonesia and Malay have similarities and differences. Malay in Malaysia and Malay in Brunei Darussalam also have differences. Mostly Malay is former of Indonesian language. But maybe around 1972 slowly Indonesian people make a big change for their language. And Malay only appears in old literature, sometimes in poetry, and very seldom we use it as daily. I give you examples:

- Some Malay words already got a bit different meaning in Indonesian"

  example: Cuti --> in Malay it means holiday. But in Indonesian 'cuti' means if take off days from our job. 'Holiday' in Indonesian is 'liburan'

- Some Malay words don't exist in Indonesian languange

 example:  'Comel' which means 'cute' in Malay never exist in standard Indonesian language

- Some Malay words have different written form with Indonesian language
example: 'beza' and 'beda'

And many others. Mostly Malay still use as daily for Indonesian people in north Sumatra. (My answer is based on my experience). I've already live in Brunei Darussalam for 2 years).

If you look back to indonesia and malaysia history you will know why they are similer...  ^^

Indonesia has so many vernaculars. More than 500 languages with Indonesian language as the national languange. Indonesian language is very similar to Malay. However, there are some languages which are very close to the Malay language, like in south Sumatra (dialect and vocabulary are almost the same).

Indonesian is 80% cognate with Malaysian and the languages (bahasa Indonesia & bahasa Malaysia) are mutually intelligible.

bahasa Indonesia and bahasa Melayu both have similarity in some vocabularies, but different in accent

All I know is the difference in accent. :) But, I found something that probably can useful for answering your question. I am sorry, if my comment doesn't help you much.