There are two types of spacing - line spacing (the space between lines in the same paragraph) and paragraph spacing (the space between adjacent paragraphs). Judging from the screenshots, the problem you are observing is with spacing after (margin-bottom in HTML). There is a bug in the current version that the default spacing after of the editor (which has 12px spacing after) is not applied to paragraphs in a table cell. This issue has been logged and you can track our progress in PITS here
. However, when exporting the document, the format provider infers the default spacing of the document and uses it when exporting the paragraphs in the table, causing them to be exported with 12 px spacing after.
What you can do is to set the ParagraphDefaultSpacingAfter of the document to 0 which will set the default spacing after to 0 and the document will look the same when viewed in the editor and exported.
I hope this information is helpful for you.
All the best,
the Telerik team