A plant will lose its blooms upon repotting if it is overly stressed.
The stress associated with repotting is related to two things:
- How much damage was done to the root system in the process (immediate- or short-term stress).
- How similar or different the root environments are, before and after repotting (longer-term stress).
If you can unpot the plant, clean off the old medium, and repot with little disturbance of the root system, there will be little immediate stress, and the plant should carry on as if nothing happened.
The closer the moisture-holding and air flow conditions between the old medium and the new, the less longer-term stress there will be. An
improvement in those conditions is also a reduction of stress. Don't forget that roots grow adapted to the conditions they are in. If the before- and after conditions are drastically different, the existing roots may not work as well, which is a stress on the plant.
On the other hand, aerial roots with those nice, fresh, growing tips will often dig down into the new medium and take over, fully supporting the plant while the older roots are supplanted by new ones branching from the old.