Justification changes when setting a type 1 font vs. setting in the otf version of the same font

I work primarily in a proprietary typeface created by a first-rate foundry/designer. The designer has assured me that character widths (with a few known exceptions) are identical in the original type 1 font and the recent otf version. Nonetheless, when we simply swap in the new version of our font (otf) for the old (type 1) font, hyphenation changes substantially. Without changing H&J settings, Indesign squeezes fully justified otf settings substantially more than it does the type 1 settings. Our H&Js permit moderate glyph scaling (99 to 101%), character spacing (-1 to +1%), and our word spacing (75–93–115) is not extreme.

Is this a known issue? I've worked in Indesign more or less since it was released, and this problem hasn't occured in the past. I’m guessing and hoping that I’m missing a simple explanation and solution. The rebreaking is a nightmare for proofreading as well as for our credibility with clients who assume that such changes may signal other inexplicable “errors.”