I would think this is an issue with whatever BD player you were using if it were doing the upconversion. Were you using the identical player for all these FPs? You can usually press an "info" or similar button on the FP to find the format of the incoming signal. BD players are almost always better at upconverting than the TV, as discussed in the following FAQ:
Here are another couple of comments.
Were you pausing the DVD? If the DVD is paused, many players will show huge "stairstepping" and other artifacts, whereas the picture can look great with the DVD playing.
What was the make/model of the BD player in question, what connection was being used and what format was it sending? Some players are much better at upconverting than others. I do not believe this was the FP, unless you tell me that the identical player was used on all the tests, with HDMI and all of the FPs were professionally calibrated. What picture mode was/were the various FPs on? Were all the FPs fed from the same BD player? If for example you were using a different player for the other FPs, then that would explain the difference.
FPs often store different picture settings for different incoming formats (rather than different inputs) since most people use only one input. Therefore if an incoming signal is 1080P, the FP could be on one picture mode, while when the signal is say 720P or 480i, the FP could be on a different mode with different settings. This could affect the image if there's too much edge enhancement for example on one signal. This would not apply if indeed the player you were using was upconverting the DVD to the same output format as the BDs.
If you have a lot of SD DVDs and you want the best picture from them, consider something like the Oppo BD player. Well reviewed for upconversion. Some BD players do not upconvert as well as others and price is often no indication of upconversion quality.