Changes of leading or paragraph spacing may behave somewhat in an unexpected way in texts that are locked to a typographical baseline grid, when such texts flow in one or more frames, or after a text without geometry gets linked to a page.
The reason is that the lock to the typographical baseline grid is not effective in text that have no geometry, ie. are not linked to a page or have no area assigned. This means that even if the lock to the typographical baseline grid exists in the assigned format, or in the applied styles, it won't be active - until you link the article to the page, or assign area to its texts.
In other words, if in a text with lock to the baseline grid applied, you apply also a leading or paragraph spacing change, either by selecting another value in the palette, or incrementing it by keyboard shortcuts, the applied value may change after you link the article to a page.
Example 1
The text, to which is applied a format that contains the lock to the baseline grid of 10pt, has no geometry.
In one or more paragraphs, you change the leading to 12pt. The leading change is effective and visible in the WYSIWYG pane - the new leading is 12pt indeed.
Now, you do one of the following:
•Link a text to a page.
•Create a local frame.
•Paste the text in another text with the same format, but linked to a page or having a local geometry.
The leading in the text reverts to 10pt.
Example 2
The text, to which is applied a format that contains the lock to the baseline grid of 10pt, flows in one or more frames.
The increment leading step is 2pt, and the current text leading is 10pt.
When you press the leading increment keyboard shortcut for the first 4 times, there is no visible effect. When you press the keyboard shortcut once again, the leading changes from 10 to 20pt.
That's because the lock to the typographical baseline grid is effective, and it locks the leading to the multiples of 10pt.