Trade Gothic is not an Adobe installed font. I think you are barking the wrong tree. Sometimes it is better to find the problem before starting shouting or you start a panic that is totally unjustified. Some older fonts were encoded wrong initially and there has previously been an acceptance to call these "symbol" encoded to get around it. In CS4 this is not done so the fonts are recoded but fragments of information remains, we process hundreds of jobs per week have not seen problembs but have heard of others that have had problems and tried to find out why, how, and how it can be avoided.
That being said, letts go back tho the initial problem you ask if there are problembs (general), but you do have a specific problem. Let me clarify.
You have problems with a document containing Trade Gothic converted from CS4 to CS3?
Do you use CS4 and CS3 on the same computer (physical)? Is it on the same platform?
Do you use font management software?
Do you have exactly the same font and font version, including afm files if you are useing metrics kerning?
Some reflowing may happen due to changes in the text engine this is not a bugg, If you make use of a feature that was not available in a previous version then it will have to be emulated, and it will require confirming the appearance. There may be tables in a font that were previously ignored and now are read, since it did contain information, so if it occurs with just one font it may be the font that has the flaw, not the program.