Round-trip export/import of Open Captions needs to be WYSIWYG.
In Adobe Premiere, Open Captions that I export out of Premiere and then immediate import back into Premiere do not match how they were exported.
Steps to repeat:
1 - In Premiere, create an Open Caption track. Create a two-line caption.
2 - Export caption using File > Export > Captions
3 - Immediately Import that caption file back into Premiere.
4 - Observe that the imported caption does not exactly match the original.
(Mostly tested in Adobe Premiere 2017, but I have verified that this problem persists in Premiere 2019 as well.)
Philip Neves commented
The SubRip format does not support that level of styling. https://en.wikipedia.org/wiki/SubRip