Reproduction steps:
1) Open a PDF file in your android acrobat reader
2) Comment it
3) Leave your file open in background (for instance, by pressing home button)
4) Seek some information required for commenting
5) Click a link
6) Realize that it opens a PDF in the Acrobat Reader
7) Pray your comment will still be there when opening the PDF you were commenting, as Acrobat Reader is known to save the comments when closing files
8) get disappointed. An hour or two of your work was lost.
9) Enter a bug report and pray it gets answered ASAP.
10) Continue being a happy Acrobat Reader user.
11) Donate at least one hour of work value in € to the fixer that will save you from losing further hours of work.