I recently created some OT/ttf fonts for an online greeting card company and am now doing a few fixes. The fonts were originally old proprietary PS fonts. Most of the fixes were just resetting vertical metrics.
The odd one in the bunch was substituting r and s with start_of_line versions. The text read: this and farrow. The s and two r's had beginning swashes and the s intruded into the space character making it look like thi sand. I cannot duplicate this on my computer. What's odd is I think the app they use for these doesn't have the capabilities for OT substitutions anyway. The three words in the sample would have had 2 ligatures if OT was functional.
Are there other issues that can cause this type of Behavior? Maybe a cache version they didn't see?