Under certain circumstances some objects that do NOT have an outline stroke set will print with one defined for other object(s) on the page.

For example, on a page with a few text frames styled with an object style that set a 2pt line stroke for outline four additional objects (PNG images) were stroked with an outline even though none of the four had an object style set, nor did they have any stroke set (it was neither 'on' or 'as is'). The document was created on linux (64-bit PgS) but printed from OS X to a color laser printer via postscript. The document appeared to load fine and displayed the page correctly in OS X.

The commonality for the mis-stroked objects is as follows: three of the four were cropped from the left and right. No other objects were cropped. The fourth object had a mask generated to run text around. No other object had a mask.

Perhaps the stroke style was erroneously set due to an artifact of how the cropping/masking was output to the printer.