In such case, CorelDRAW will re-build the bitmap and you will get a new bitmap in the exported file.
You can find our hidden function in the bitmap Context menu:
Right-click the bitmap >Save Bitmap As
he name - Save Bitmap As as distinct from Export – implies that it will save the bitmap to disk. In fact it does not; it will export (re-build) it to a new bitmap according to the new properties you set in the Export and Convert to Bitmap dialogs.
Fair Solution Conclusion :'(
The hidden Save Bitmap As = Export Selected only
Solution Conclusion

To extract a bitmap from CorelDRAW page and save it as a bitmap file (JPG, PNG, GIF…):
Select the bitmap
On the Property bar, click the Edit Bitmap button
From Corel PHOTO-PAINT, Save the bitmap As or Export